1、The PracticalReference Guide toCommercial Applications550 N.W. LeJeune Road, Miami, Florida 33126THE PRACTICALREFERENCE GUIDEtoWELDING ALUMINUMinCOMMERCIAL APPLICATIONSCompiled/Edited/Written byFrank G. ArmaoGroup Leader, Nonferrous ApplicationsThe Lincoln Electric CompanyThis publication is designe
2、d to provide information in regard to the subject matter covered. It is made availablewith the understanding that the publisher is not engaged in the rendering of professional advice. Reliance uponthe information contained in this document should not be undertaken without an independent verification
3、 ofits application for a particular use. The publisher is not responsible for loss or damage resulting from use of thispublication. This document is not a consensus standard. Users should refer to the applicable standards for theirparticular application.iiPhotocopy RightsAuthorization to photocopy i
4、tems for internal, personal, or educational classroom use only, or the internal,personal, or educational classroom use only of specific clients, is granted by the American Welding Society(AWS) provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive,Danvers, MA
5、 01923, Tel: 978-750-8400; online: http:/. 2002 by the American Welding Society. All rights reserved.Printed in the United States of America.AUTHOR NOTESUltimately, I would like to thank Bob Schneider, who is an old friend of mine, for making this book happen.A couple of years ago, I was asked by De
6、brah Weir of AWS to review a similar book that Bob had written ti-tled “The Practical Guide for Welding Aluminum: High Quality Fusion Welding.” My review concludedthat, while Bobs book captured his long and varied experience in the aerospace industry, it didnt includepractices common in other, highe
7、r production volume industries. The next thing I knew, Bob and Debrahsuggested that I cover those industries in a separate volume, which became this book. With additional en-couragement and support from Debrah, who is Corporate Director of New Product Development for AWS,and Lee Kvidahl, an AWS past
8、 president and the current chair of the AWS Product Development Committee,this book has become a reality. Thank you both for your patience and help.I would also like to thank Dr. Toby Pearlstein of Bain however, no direct reduction method,such as that used to make steel, was found to pro-duce alumin
9、um from bauxite until 1886, when theAmerican, Charles M. Hall, and the Frenchman,Paul Heroult, almost simultaneously, yet indepen-dently, discovered electrolytic processes for obtain-ing pure aluminum from aluminum oxide. As aresult, aluminum became available in commercialquantities. These processes
10、, with some modifica-tions, are still used today.Since that time, aluminum has found wide use innumerous applications: It conducts electricity and heat almost as well ascopper.It is widely used in electrical bus bars and otherconductors, heat exchangers, and cookware.It does not become brittle with
11、decreasing tem-perature, but instead becomes stronger, so it hasfound wide application in cryogenic equipmentat temperatures as low as 452F.It is very corrosion resistant in most environ-ments, so it has found wide applications in ma-rine and chemical environments.The characteristics of aluminum all
12、oys, whichmake them attractive as structural materials formany applications, are their light weight (one thirdthe weight of steel for equal volumes) and their rel-atively high strength (equal in many cases to that ofconstruction steel grades). This combination has re-sulted in increased use of alumi
13、num alloys in appli-cations such as automobiles, trucks, over-the-roadtrailers, and railroad cars. Additionally, the struc-ture of most aircraft is fabricated mainly from alu-minum alloys, although in this application, piecesare most often joined by riveting.Welding Aluminum vs. Welding SteelMost in
14、dustrial welders start out by learning howto weld steel; a minority later move on to weldingaluminum. Since most welding equipment is de-signed to weld steel, the welding of aluminum al-loys is frequently just an afterthought. However,this attitude is changing.The welding of aluminum is often approa
15、ched asthough aluminum were just shiny steel. However,there are definite differences between the weldingof steel and aluminum. This guide will discussthese differences and how to overcome the prob-lems that arise when the welding of aluminum isconsidered to be the same as the welding of steel.Three
16、common fallacies are as follows:(1) If you take enough care almost all steels are weldable.Fabricators regularly fall into this trap. There aresome aluminum alloysespecially the strongeronesthat are just not arc weldable.(2) All steels are heat treatable.Some aluminum alloys are heat treatable, but
17、somearent. Even for the heat-treatable aluminum alloys,the heat treatments are totally different from thoseused for steel. In fact, if you heat some alloys andthen quench them, they become softer, not harder.Be aware of the differences and act accordingly.(3) When welding steels, you can almost alwa
18、ys make aweld that is as strong as the parent material.In aluminum alloys, the weld will rarely be asstrong as the parent material. This is usually truefor welds in both heat-treatable and nonheat-treatable alloys. The strength difference betweenthe weld or heat-affected zone (HAZ) and the par-ent i
19、s significant, often 30% or more.Aluminum Alloy and Temper DesignationsMuch in the same manner that the American Ironand Steel Institute (AISI) registers steel chemistriesand grades, the Aluminum Association (AA) regis-ters alloy designations, chemistries, and mechanicalproperties for aluminum alloy
20、s. However, the alloydesignation system is totally different than thatused for steels. Additionally, different systems areused for wrought and cast alloys.2 AWS Practical Reference GuideWelding Aluminum in Commercial ApplicationsWrought AlloysWrought alloy designations use a four-digit num-ber, plus
21、 a temper designation. All aluminum alloyshave been divided into eight “families” dependingon the main alloying elements. The aluminum alloyfamilies are shown in Table 1, along with their heattreatability.For example, if you have a piece of 6061, accordingto Table 1, the 6061 is a wrought alloy (4 d
22、igits) thatis heat treatable, and contains magnesium and sili-con. The second digit shows whether the alloy isthe first such alloy registered (in which case the sec-ond digit will be “0,” as in 5054). Digits other than“0” indicate that the alloy is a modification of a reg-istered alloy, i.e., 5154 i
23、s the first modification of5054, and 5754 is the seventh modification. The lasttwo digits are assigned arbitrarily by the Alumi-num Association when the alloy is registered. Notethere is no indication of alloy or weld strengthgiven by the material designation.Cast AlloysThe designation system for ca
24、st alloys is shown inTable 2. The specific families are somewhat differ-ent from the designations for wrought alloysthese designations have only three digits, followedby a decimal point and another digit. For cast alloysthe first digit shows the alloy family. The next twodigits are arbitrarily assig
25、ned. Alloy modificationsare shown by a letter prefix; therefore, 356 is theoriginal version of an alloy and A356 is the firstmodification, B356 is the second modification, etc.The number following the decimal point designateswhether the alloy is produced as a casting of finalform or is produced as a
26、n ingot for re-melting.Temper DesignationsThe preceding information allows the alloy to be rec-ognized by its chemistry, but not by the heat treat-ment or mechanical properties. To show theseproperties, temper designations are assigned. Thecomplete designation of an alloy might be 6061-T6 or5083-H11
27、4. Most of these designations are differentfor heat-treatable and nonheat-treatable alloys; how-ever, two common designations apply to all alloys:(1) “O” Temper (not the number zero). When analloy is given this designation, the supplier has an-nealed the alloy (typically at 650750F), and thealloy is
28、 as soft and weak as possible.(2) “F” Temper. An alloy supplied in this temper issupplied “as fabricated.” The supplier guaranteesthat the chemistry of the material meets the chemi-cal requirements for the specified alloy, but thereare no claims regarding the mechanical propertiesof the alloy. This
29、temper is often specified by fabri-cators who subsequently forge or form the suppliedmaterial and establish mechanical properties byheat treatment after forming.Table 1. Destination system for wrought alloys.AlloyFamily Main Alloying ElementsHeatTreatable1XXX Pure Aluminum No2XXX Copper (sometimes w
30、ith magnesium) Yes3XXX Manganese (sometimes with magnesium) No4XXX Silicon No5XXX Magnesium No6XXX Magnesium plus silicon Yes7XXX Zinc (sometimes with magnesium and copper)Yes8XXX All others NormallyYesNOTE: The designation 2XXX, etc. is an industry standardabbreviation used to mean “all the alloys
31、in the 2000 series.”Table 2. Designation system for cast alloys.AlloyFamily Main Alloying ElementsHeat Treatable1XX.X Pure Aluminum No2XX.X Copper Yes3XX.X Silicon plus magnesium Yes4XX.X Silicon Yes5XX.X Magnesium No6XX.X Not Used NA7XX.X Zinc Yes8XX.X Tin No9XX.X OtherWelding Aluminum in Commercia
32、l ApplicationsAWS Practical Reference Guide 3Nonheat-Treatable AlloysStrain-Hardened DesignationsThese alloys can not be strengthened by heat treat-ment. However, they can be strengthened by coldworking, also called “strain hardening.” If an alu-minum alloy is deformed at elevated temperatures(600F
33、or higher), little or no strengthening takesplace. However, if the alloy is deformed at lowertemperatures, it will gain strength. In general:(1) The more an alloy is deformed, the stronger itbecomes. At some point, the alloy will have no duc-tility left and will fracture.(2) The higher the alloy con
34、tent, the more an alloywill gain strength by being deformed.Both of these phenomena are shown in Figure 1.The temper designation for strain-hardened alloys isusually made up of two digits as shown in Figure 2.The first digit shows whether the alloy is onlystrained or whether it has been partially an
35、nealedand/or stabilized. The second digit shows the de-gree of strain hardening. Higher numerical valuesmean higher strain levels, which mean higher yieldand tensile strengths.Heat-Treatable AlloysThe strain-hardened H tempers are not used forheat-treatable alloys. Instead, a series of T tempersindi
36、cating the heat treatment state are used. A totalof 10 tempers exist, T1 through T10. However, thetempers commonly seen are T4 and T6.Aluminum alloys are heat treatable because of aphenomenon called “precipitation hardening.”Aluminum alloys do not harden by a martensitictransformation as steel does.
37、 In precipitation hard-ening, one metal can be dissolved in another in a“solid solution” and solubility generally increaseswith temperature. For example, just as sugar dis-solves in a glass of iced tea when heated, copper orzinc or combinations of magnesium and silicon willdissolve in aluminum as it
38、 is heated.When heat-treatable alloys are heated to approxi-mately 950F and held for a few minutes, all the al-loying elements are taken into a solution in the solidaluminum. This is termed a “solution heat treat-ment.” Normally, the alloy is quenched in waterfrom this point to arrive at the T4 temp
39、er. Althoughthe T4 temper is substantially stronger than the an-nealed O temper, the primary purpose of quenchingis not strengthening. Instead, the quenching servesto keep the alloy additions in solution at room tem-perature, because if the aluminum were cooledslowly from the solution treatment, the
40、 alloyingadditions would re-precipitate and no strengthen-ing would occur.The tensile and yield strengths of T4 material willincrease for several weeks after the heat treatmentand, in some alloys, will increase significantly.However, once past this initial period, the T4 alloyis stable indefinitely.
41、 The user normally is unawareFigure 1. The relationship of yield strength, amount of cold work, and alloy content.TEMPERSPERCENT COLD WORKYIELDSTRENGTH(ksi)MPa100200300502040301000 20 40 60 8011005052508630030 H12 H14 H16 H18H38H36H34H32The first digit indicates basic operations:H1strain hardened on
42、ly.H2strain hardened and partially annealed.H3strain hardened and stabilized.The second digit indicates degree of strain hardening:HX2quarter hard.HX4half hard.HX6three-quarters hard.HX8full hard.HX9extra hard.The third digit indicates a variation of a two-digit temper.Figure 2. The “H” temper desig
43、nations forstrain-hardened alloys.4 AWS Practical Reference GuideWelding Aluminum in Commercial Applicationsof this initial strength increase, because the alumi-num producer doesnt ship the alloy until thestrength has stabilized.The T4 temper, while stable, does not give maxi-mum strength to the all
44、oy. Most alloys are sold in amaximum strength T6 temper. To get from T4 to T6temper, put the material in a furnace at a tempera-ture of 325400F and allow it to age from 15 hours.The dissolved alloying elements will form submi-croscopic pre-precipitates in the material and pro-duce maximum strength.
45、If this aging heattreatment is carried out at high temperatures for anextended period, the precipitates will get too largeresulting in a lower strength “overaged” condition.Note: This final aging heat treatment is carried out at400F maximum. The welding heat, which can heat thesurrounding material t
46、o well over this temperature, cansignificantly degrade the strength of the weld HAZ.Effect of Welding on Mechanical Properties of Aluminum AlloysThe effects of welding on the mechanical propertiesof aluminum weldments can be best understoodby discussing nonheat-treatable alloys and heat-treatable al
47、loys separately.Nonheat-Treatable AlloysCold-worked alloys can have yield and tensilestrengths twice those of the annealed “O” temperalloys. These cold-worked alloys can be softenedback to the “O” temper by annealing at 650700F.Since the heat of welding produces temperaturesconsiderably higher than
48、this at the weld fusionline, the result of welding is that the HAZ of weldsin nonheat-treatable alloys (i.e., 1XXX, 3XXX, 4XXX,and 5XXX) becomes annealed. Therefore, thestrength of the weld joint is always equal to thestrength of the “O” temper annealed base material,regardless of the starting tempe
49、r of the parent material. Ifyou weld “O” temper material, the weld will be asstrong as the starting parent material. If you weldany material that is strain hardened (i.e., coldworked), the weld can be significantly weaker thanthe starting material.Since the HAZ can never become softer than the“O” temper, any excess welding heat input will notmake the HAZ softer. It can, however, make theHAZ wider. Normally, this will not further reducethe strength of the welded joint, although otherproblems can arise due to excessive heat input.From a practical
