Arc Welding Aluminum Alloys 340

AC

Alternating current. Electricity that switches direction at regularly recurring intervals of time. AC is typically used to reduce heat and for cleaning properties.

AC aluminum pulse welding

An advanced GMAW process that uses alternating current (AC) and a pulse waveform to weld aluminum. AC aluminum pulse welding has a lower heat input because of the alternating polarity of AC.

aged

Heated to a certain temperature to cause a change in grain structure. Metals are usually aged to increase their hardness.

alloying elements

A material that is intentionally added to a metal in order to change its properties. Alloying elements can improve the strength, ductility, hardness, and toughness of a finished weld.

alloys

A material consisting of a mixture of two or more elements, one of which must be a metal. Alloys combine the beneficial properties of the mixed elements.

alternating current

AC. Electricity that switches direction at regularly recurring intervals of time. Alternating current is typically used to reduce heat and for cleaning properties.

aluminum

A lightweight, highly conductive, nonferrous, silvery metal. Aluminum has good weldability, but certain factors, such as its melting point, can make the process difficult.

aluminum oxide

A thin film that forms on the surface of aluminum when it reacts with oxygen in the air. Aluminum oxide must be removed before welding.

amperage

The amount of current flowing in a circuit. Amperage is measured in amperes (A), or amps.

amperes

A. The unit used to measure current or amperage. Amperes are also called amps.

arc

The area in which electricity transfers from the electrode to the workpiece. The heat generated by the arc melts the base metals and filler metal during welding.

arc starting

The process of initiating an electric arc between the welding electrode and the workpiece. Arc starting is typically done by touch-based methods or non-contact methods like high-frequency starting.

argon

A heavy inert gas commonly used for shielding in arc welding processes. Argon is much heavier than air, so it effectively shields the weld area.

backing strips

A strip of metal located on the side opposite of the weld. Backing strips protect the back of the weld from atmospheric contamination and provide a surface for depositing the first layer of metal.

balling

An electrode preparation process in which the tip of the tungsten electrode is formed into a sphere. Balling is easiest to perform on pure and zirconiated tungsten electrodes.

base metal

One of the metals welded together to form a joint. The base metal and its properties influence the weld type, welding process, and electrode.

beveling

A metal removal process that produces an angled surface on the edge of an object. Beveling allows welders to access joints made from thicker base metals more easily.

burnback

A condition that occurs when electrode wire melts back and fuses to the contact tip. Burnback can stop wire feeding, clog nozzles, and interrupt welding.

burnthrough

A discontinuity that occurs when weld metal from one side of a joint melts through to the other side. Burnthrough can leave an open hole in the joint, which must then be ground down and re-welded.

butt

A joint created between two parts that lie in the same plane. Butt joints are simple, common joints.

carbon dioxide

A heavy active gas commonly used for shielding in arc welding processes. Carbon dioxide is inexpensive but yields a violent arc.

carbon steel

The most basic form of steel, which contains less than 3.0% alloying elements. Carbon steels are divided into low-, mild, medium-, and high-carbon steels.

cast alloys

An alloy that has been poured as a liquid into a mold and cooled into a solid shape. Cast alloys are often difficult to weld because they are prone to defects.

centerline cracks

A longitudinal fracture in the middle of a weld at the weld face. Centerline cracks may be caused by improper width-to-depth ratio or improper welding techniques.

ceriated

A tungsten electrode that contains a small percentage of cerium. Ceriated electrodes are usually 2% cerium and 98% tungsten and may be used as a replacement for thoriated tungsten.

chrome

A hard gray metal that is highly resistant to corrosion and wear. Chrome may be applied to wire feeder drive rolls for a smoother surface.

cold working

The shaping of metal at temperatures below the recrystallization temperature. Cold working is used most often with malleable, ductile metals.

constant current

CC. A power supply in which the amperage is set at a fairly fixed level and varies only slightly with changes in voltage. Constant current power sources are often used in gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW).

constant voltage

CV. A power supply in which the voltage is set at a fixed level and the amperage varies to maintain relatively constant voltage. With constant voltage, the wire feed speed (WFS) is also set at a fixed rate and maintained by the varying amperage.

contact tip to work distance

CTWD. The distance from the contact tip of the welding gun to the workpiece surface. Contact tip to work distance combines electrode extension and arc length.

contact tips

The component located inside the welding gun that conducts electricity to the electrode. The contact tip is usually made of copper.

continuous wire feeding

A metal transfer mode in which filler wire maintains constant contact with the molten weld pool. Continuous wire feeding is primarily used in automatic wire fed GTAW to enhance stability.

copper

A reddish metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper-aluminum alloys are difficult to weld and often used for aircraft components.

corner

A joint created between the edges of two workpieces that are often located at right angles to one another. Corner joints require large amounts of filler metal.

corrosion resistance

The ability of a material to resist deterioration and chemical breakdown due to surface exposure to certain conditions. Corrosion resistance is a positive quality of aluminum and aluminum welds.

crater cracks

A small fracture in the center of a depression in the weld face. Crater cracks can be prevented by filling in any craters or using a backstep technique when terminating the weld.

cycle

The process of alternating current changing direction and then returning to its original direction of flow. During welding, an AC cycle contains an electrode positive (EP) stage and an electrode negative (EN) stage.

DC

Direct current. Electricity that flows in one continuous direction. DC is required for several common welding processes.

defects

An irregularity in the specified and expected composition of a weld that exceeds the part design's tolerances. A defect is an unacceptable discontinuity.

degreasers

A solvent formulated to break down and remove contaminants like grease, oils, and other coatings from materials. Degreasers can be used to remove aluminum oxide before welding.

deposition rates

The rate at which an electrode melts into the molten weld pool to form a weld. Deposition rate can be measured in pounds per hour or in grams per minute.

die casting

A thermal, high-pressure metal casting process that involves injecting molten metal into a mold at high velocity and pressure. Die casting is a metal shaping process used in traditional manufacturing.

dipping technique

A GTAW filler metal addition technique in which the welder repeatedly dips the end of the filler rod into the weld pool. The dipping technique is typically used when running stringer beads to better control heat input.

direct current

DC. Electricity that flows in one continuous direction. Direct current is required for several common welding processes.

direct current electrode negative

DCEN. Electricity that always flows in one continuous direction from the negative electrode to the positive workpiece. Direct current electrode negative polarity is also known as straight polarity, but this is a nonstandard term.

direct current electrode positive

DCEP. Electricity that always flows in one continuous direction from the negative workpiece to the positive electrode. Direct current electrode positive polarity is also known as reverse polarity, but this is a nonstandard term.

discontinuities

A flaw or imperfection in the specified and expected structure of a part or material. Discontinuities are not always defects.

distortion

The non-uniform expansion of weld metal during the heating and cooling process of welding. Distortion can be caused by using incorrect welding variables.

drag angle

A travel angle that points the electrode opposite the direction of travel. Drag angles are used with the backhand technique.

drawing

A forming process that shapes parts by stretching metal around a punch and forcing it into a die cavity. Drawing operations are often used to create parts with complex contours, such as automotive body panels.

drive rolls

A wheel that directs the wire electrode as it moves through a wire feeder. Drive rolls are specially designed for various types and sizes of wires.

ductility

A material's ability to be drawn, stretched, or formed without breaking. Ductility is more common in softer metals.

electrical conductivity

The ability of a material to act as a medium for conveying electricity. Electrical conductivity is high for most metals.

electrode

A conductor used to establish electrical contact in a circuit. Welding electrodes can act as filler metal.

electrode negative

EN. The stage of the alternating current cycle during which electricity flows from the negative electrode to the positive workpiece. The electrode negative stage concentrates heat in the workpiece and improves penetration.

electrode positive

EP. The stage of the alternating current cycle during which electricity flows from the negative workpiece to the positive electrode. The electrode positive stage improves fusion and provides a cleaning effect for some processes.

EP

Electrode positive. The stage of the alternating current cycle during which electricity flows from the negative workpiece to the positive electrode. The EP stage improves fusion and provides a cleaning effect for some processes.

excessive penetration

A weld discontinuity that occurs when too much heat is applied to the weld zone, causing the weld metal to fall through the joint. Excessive penetration includes burnthrough.

extrusion

A molding process that forces raw material through a die opening. Extrusion is a continuous process that can create parts with a uniform cross-section.

filler metal

Metal deposited into the weld that often adds strength and mass to the welded joint. Filler metal may come from the electrode, like in GMAW, or a separate filler rod, like in GTAW.

forging

A forming process that involves compressing a metal at elevated temperatures. Forging creates very strong parts due to their compressed grain structure.

frequency

A measurement of the number of times a waveform repeats in one second. Frequency is measured in hertz (Hz) or cycles per second.

furnaces

A self-contained metal structure that can be heated to exceptionally high temperatures. Specialized furnaces can be used to preheat base metals before welding.

fusion

The joining of base metals and any filler metal during welding. Fusion can be impacted by contaminants.

gas metal arc welding

GMAW. An arc welding process in which a wire electrode and shielding gas are fed to the weld through a welding gun. Gas metal arc welding is also referred to as metal inert gas (MIG) welding or metal active gas (MAG) welding, although these terms are nonstandard in the United States.

gas nozzle

A device attached to the front of a GTAW torch body that directs shielding gas over the weld area. GTAW gas nozzles are sometimes referred to by the nonstandard term cup.

gas tungsten arc welding

GTAW. A precise arc welding process that uses a non-consumable tungsten electrode and inert shielding gas. Gas tungsten arc welding is also known as tungsten inert gas (TIG) welding, although that term is nonstandard in the United States.

GMAW

Gas metal arc welding. An arc welding process in which a bare wire electrode and shielding gas are fed to the weld through a welding gun. GMAW is also referred to as metal inert gas (MIG) welding or metal active gas (MAG) welding, although these terms are nonstandard in the United States.

grain boundaries

The place where two grains meet. Grain boundaries help determine the microstructure of a metal.

grain structure

The size, arrangement, and orientation of the small, hard particles in a metal or alloy. Grain structure, also known as microstructure, helps determine the properties of a metal.

grinding

Using an abrasive to remove material from the surface of a part. Grinding is usually performed using abrasive wheels.

groove angles

The angle of the groove between two workpieces being welded together. Groove angles must be wide enough to accommodate welding gun or torch manipulation.

groove face

The exposed surface of the groove between two workpieces. The groove face must experience complete fusion to create a quality weld.

GTAW

Gas tungsten arc welding. A precise arc welding process that uses a non-consumable tungsten electrode and inert shielding gas. GTAW is also known as tungsten inert gas (TIG) welding, although that term is nonstandard in the United States.

HAZ

Heat-affected zone. The portion of the base metal immediately surrounding the weld metal zone. The HAZ does not melt during welding, but its mechanical and physical properties are altered.

heat dissipation

The loss or transfer of heat. Heat dissipation can help control thermal expansion.

heat input

The amount of thermal energy transferred to the workpiece during welding. Heat input is measured in kilojoules per inch (kJ/in.) or kilojoules per millimeter (kJ/mm).

heat sink

A block of thermally conductive material placed tightly against a metal joint. Heat sinks absorb excess heat from the workpiece to prevent burnthrough, and distortion on thin metals like aluminum.

heat treatment

Any controlled heating and/or cooling process used to change the structure of a material and alter its physical and mechanical properties. Heat treatment processes include preheating and post-heating processes.

heat-affected zone

HAZ. The portion of the base metal immediately surrounding the weld metal zone. The heat-affected zone does not melt during welding, but its mechanical and physical properties are altered.

heating torches

A device that uses the controlled combustion of fuel gases to produce a flame. Heating torches are used to preheat base metals for welding.

heat-treatable

An alloy that can be heated before, during, or after welding to preserve or restore its strength and hardness. Heat-treatable aluminum alloys include copper, magnesium-silicon, and zinc alloys.

helium

A lightweight inert gas commonly used for shielding in arc welding processes. Helium is much lighter than air and can escape the weld area quickly.

high-frequency start

An arc starting method that uses a high voltage to generate a spark between the electrode and the workpiece. For the high-frequency start method, the welder holds the electrode near the workpiece and uses a control device to start a high-frequency current that provides the spark.

hot cracking

The formation of fractures in a weld due to stress placed on thin materials or materials with low tensile strength during solidification. Aluminum and aluminum alloys often experience hot cracking.

hydrocarbons

A chemical compound that contains only hydrogen and carbon. Hydrocarbons can contaminate aluminum welds.

hydrogen

A colorless, odorless gas that is the most abundant element on the planet. Hydrogen can cause cracking and porosity in weld metal.

ingot

A solid block of metal cast into a simple shape, such as a bar or sheet. Ingots are considered unfinished and require additional machining, processing, and finishing.

inverter

An electrical device that uses transistors to increase the frequency of supplied electricity and convert DC to AC. Inverters allow welding power sources to be smaller and more efficient.

inverter power sources

A welding machine that uses a series of components including inverters and transistors to convert input electricity to usable power. Inverter power sources are small, portable, and energy-efficient, but expensive.

lanthanated

A tungsten electrode that contains a small percentage of lanthanum. Lanthanated electrodes are typically 1-2% lanthanum.

lap

A joint created between the edge of one part and the surface of an overlapping parallel part. Lap joints provide more stress resistance than butt joints.

liner

The insulated lining that surrounds the electrode and supports it from the wire feeder to the contact tip of the welding gun. Electrode liners are often used for aluminum and can be either permanent or interchangeable.

magnesium

A grayish-white, extremely light metal that is brittle and has poor wear resistance. Magnesium can be combined with aluminum to create a strong alloy with excellent weldability.

manganese

A hard, brittle, gray-white nonferrous metal often added to electrodes. Manganese acts as a deoxidizer and increases strength and hardness in aluminum alloys.

mechanical properties

A characteristic of a material that describes its ability to compress, stretch, bend, scratch, dent, or break. Mechanical properties include tensile strength and yield strength.

melting point

The temperature at which a material changes from a solid to a liquid. Melting point varies based on the properties of the material.

metal transfer

The deposition of filler metal into a weld. Metal transfer methods differ depending on the welding process and current density.

milling

A machining process in which a rotating multi-point cutting tool is fed along a part's surface to remove material. Milling operations typically produce flat surfaces.

molds

A hollow cavity used to shape material. Molds are filled with liquid material, which takes the shape of the mold as it solidifies.

nitrogen

A colorless, odorless, tasteless gas that naturally makes up 78% of breathable air. Nitrogen can ruin a weld bead.

nonferrous

A metal that does not contain a significant amount of iron. Common nonferrous metals include aluminum, titanium, copper, and nickel.

non-heat-treatable

An alloy that relies primarily on cold working to increase its strength and hardness. Non-heat-treatable aluminum alloys include manganese, silicon, and magnesium alloys.

nylon

A semicrystalline thermoplastic that gains strength when the fibers are stretched. Nylon can be used as an electrode liner.

overlap

A discontinuity that occurs when the weld metal protrudes beyond the weld toe or weld root. Overlap is nearly always unacceptable in a finished weld.

oxygen

A colorless, odorless, tasteless gas that naturally exists in the atmosphere. In welding, too much oxygen causes cracking and rusting in metals.

peening

Using a tool to harden or stretch a surface by striking it. Peening hammers are also known as ball-peen hammers or machinist's hammers.

penetration

The depth to which the arc heat melts the joint below the surface of the base metals. The amount of amperage directly affects weld penetration.

polarity

The state of having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

porosity

A weld discontinuity characterized by the appearance of tiny voids in a weld bead, which occurs when gas is trapped in the metal. Excessive porosity can weaken a weld.

post-heating

The application of heat to a weld immediately after welding, before the weld has cooled. Post-heating helps reduce stress in the weld metal.

post-weld heat treatment

PWHT. The process of heating a weld after welding is complete and the weld has cooled. Post-weld heat treatment reduces stress in the welded metal.

power source

The device that provides the electricity needed to perform arc welding. Power sources may also contain a wire feeder.

precipitate

To separate elements from a solution. Elements that precipitate out of a solution change the properties of a metal.

precipitation hardening

The process of producing hardness and strength in an alloy through a series of controlled heating and cooling processes. The precipitation hardening process includes solution heat treating, quenching, aging, and cooling.

Preheating

The application of heat to a base metal immediately before welding. Preheating provides several benefits, such as reducing hardness, improving ductility, and decreasing the likelihood of hydrogen cracking.

pressure vessels

A container designed to hold liquids or gases at high pressures. Pressure vessels include gas cylinders and propane tanks.

pulsed spray transfer

GMAW-P. An advanced GMAW mode of metal transfer that alternates rapidly between different current levels to precisely form metal droplets. During pulsed spray transfer, one droplet of metal is deposited during each cycle.

pulsed wire feeding

A metal transfer mode in which filler wire periodically touches the weld pool. Pulsed wire feeding is primarily used in automatic wire-fed GTAW.

push angle

A travel angle that points the electrode in the direction of travel. Push angles are used with the forehand technique.

push system

A wire drive system that uses a single, high-torque motor located in or on the welding machine to move the filler wire from a spool into the gun. Push systems are commonly used for rigid, shorter wire.

push-pull system

A wire drive system that uses one motor to push the electrode out of the wire feeder and another motor to pull the electrode through the welding gun. Push-pull systems are often used when welding aluminum.

quenched

Rapidly cooled through the use of oil, water, or air. Quenched metals retain the grain structure they developed before quenching.

rolling

A forming process in which a sheet of metal is passed through rollers to reduce thickness and make the sheet a uniform size. Rolling can also be used to improve the properties of a workpiece.

root

The point at which a weld intersects the surfaces of the base metals opposite the face of the weld. Some welds have openings located at the weld root.

root openings

The separation between base metals at the root of a weld. The size of the root opening determines how much weld metal is needed to obtain fusion at the root.

shielding gas

A gas that protects the weld pool and arc from reacting negatively with the atmosphere. Shielding gas is supplied by a cylinder or tank and flows through the welding gun.

shrinkage

The reduction in size that a part experiences as it contracts while cooling after exposure to intense heat. Shrinkage can change the microstructure of metal and plastic parts.

silicon

A nonmetallic material that is often present in arc welding electrodes and flux. Silicon acts as a deoxidizer and alloying element in some alloy aluminums.

solubility

The measure of the amount of a substance that will dissolve in a liquid. A substance's solubility depends on the solvent being used, as well as temperature and pressure.

solution heat treatment

The first step of precipitation hardening in which an alloy is heated to a temperature high enough to allow the alloying element to form a solution with the base metal. Solution heat treatment increases the metal's hardness.

spatter

Liquid metal droplets expelled from the welding process. Spatter can leave undesirable dots of metal on the surface of a workpiece.

spool gun

A welding gun with an integrated wire drive system that feeds wire from self-contained spools mounted on the gun. Spool guns are mainly used for smaller-diameter, softer wires, such as aluminum.

spray transfer

A GMAW mode of metal transfer in which the metal at the end of the electrode melts into small, fine droplets that transfer to the weld pool. Spray transfer creates a stable arc and little spatter.

stainless steel

A type of alloy steel that contains a large percentage of chromium. Stainless steels exhibit excellent corrosion resistance and high strength.

strength-to-weight ratio

The relationship between a material's strength and its weight. Strength-to-weight ratios are considered high when a metal is light and strong.

stringer beads

A weld bead formed by moving the electrode in a straight line along the joint. Stringer beads can also be created by using a slight back and forth motion.

T

A joint created between the edge of one part and the surface of a second, perpendicular part that resembles the letter "T." T-joints are very common joints that are simple to create.

tack welds

A temporary weld that holds workpieces in proper alignment for a final welding process. Tack welds are also used to aid in preheating.

Teflon

A fluorocarbon solid that may be used to coat surfaces. Teflon, also referred to as polytetrafluoroethylene (PTFE), can be used as an electrode liner.

tempered

Metal that has been reheated to intermediate temperatures and then gradually cooled in order to harden its outer surface. Tempered metals usually have improved toughness.

tensile strength

A material's ability to resist forces that attempt to pull it apart or stretch it. Materials with high tensile strength tend to deform, bend, or stretch before breaking.

tensile stress

A force that attempts to pull apart or stretch a material. Tensile stress produces cracks during thermal stress cracking.

thermal conductivity

The ability of a material to act as a medium for conveying heat. Materials with superior thermal conductivity include aluminum and copper.

transformer power sources

A welding machine that uses a large transformer to convert input electricity to usable power. Transformer power sources are large and inefficient.

travel speed

The rate at which the electrode moves along the joint to make a weld. Travel speed determines the size of the weld bead.

tungsten

A dense, brittle, gray metal that has excellent conductivity and the highest melting point of all pure metals. Tungsten is used to make non-consumable electrodes for GTAW.

U-groove welds

A groove weld made in an opening shaped like the letter “U." U-groove welds use base metals with concave edges.

V-groove welds

A groove weld made in an opening shaped like the letter "V." V-groove welds use base metals with angled edges.

wave balance

A setting on advanced welding power sources that controls the time that the alternating current spends in electrode negative or electrode positive. Wave balance controls the efficiency of the cleaning action and the depth of penetration.

weave beads

A weld bead formed by moving the electrode side to side along the joint in an oscillating motion. Weave beads generally require too much heat for aluminum welding.

weld bead

The end product of a single weld pass. Weld beads are formed using a variety of different techniques.

weld face

The exposed surface of a weld. The weld face may be convex, concave, or flush with the workpiece.

weld pool

The small area of molten metal that forms during welding and that, when cooled, forms the permanent joint. Weld pools are sometimes called weld puddles.

weldability

The ability of a material to be welded into a suitable structure. Weldability is generally higher in non-heat-treatable alloys than heat-treatable alloys.

wet

The process of a liquid filler metal spreading over a solid surface. Molten metals that wet easily create smooth welds.

WFS

Wire feed speed. The rate at which the wire electrode is fed through the contact nozzle. WFS is measured in inches per minute or millimeters per minute.

wire brush

A tool with wire filaments used to clean the surface of a workpiece. Wire brushes can remove impurities that could contaminate the weld and cause defects.

wire drive systems

The device that feeds a supply of wire electrode to the welding gun. Wire drive systems are typically either built inside a power source, mounted to the power source, or part of the welding gun.

wire feed speed

WFS. The rate at which the wire electrode is fed through the welding gun. Wire feed speed determines amperage and the amount of heat in the arc in GMAW.

wire feeder

The device that feeds a supply of wire electrode to the welding gun. The wire feeder may be either built inside the power source or an external device set beside it.

work hardening

The process of increasing the hardness of a metal by bending or shaping it. Work hardening processes include cold working and case hardening process.

wrought alloys

An alloy that has been physically formed into a desired shape. Wrought alloys are preferred for welding aluminum due to their strength, ductility, and uniform grain structure.

zinc

A bluish-white metal that is corrosion resistant and has a relatively low melting point. When used as an alloying element, zinc forms the strongest heat-treatable aluminum alloy.

zirconiated

A tungsten electrode that contains a small percentage of zirconium. Zirconiated electrodes are typically 0.3% or 0.8% zirconium and may be used as a replacement for thoriated tungsten.