Effect of weld parameters on the properties of aluminium weldment

Abstract

Two different grades of aluminium pbtc> (lxxx and 5xxx ,.r1es) were welded \.ith two different filler metals (4043 and 5356) and with dIfferent current settmgs of 145A, 175/\ and 195A. Tung,ten Inert Gas ('1'10) welding process was used [or welding. Durmg weld"'g at dlffcrcnt conditions various eutectics, in!erme!allLc compounds and phases formed at dllTcrcm temperatures and at difTerent compositions. All of these phases contributed 10 a change Ln mechanical properties. In (he present research, a systematic mvcsllgMion was made on TIG welding of aluminium alloy to determine the probable reasons for evolutlon of ,olJdlli"allOn cracking of aiummmm weld and to improve the ,tructure- propel ty relalloosh,p "f wddmenl by controlling he"! input. It wa, expected that thc rcscar~h work will optlmL7.e (he process parameter to find out an 0pllmum condition for welding, When 4043 filler metal (Al-5% Si) was used for welding pure alummlum plate, (lxxx ,crie,) a secondary phase fonned during weldmg. It wn,; ld~nllficd ns AI-Si eutectiC nuxlurc and was different in :;ize, shape and orienlat'on not only ~t dlffcrml current seltmg but also al dlffercnl location of the welded sample,_ Jt was observed that a( lhe highest current selling lhal lS "t the highesl heat input the eulectic mixture was coarsest and largest in Sl7e and tends 10 [(}ml " continuous network, On the other hand at low heat Lnputs the eutectic mixlure d,d nol get sufficient time to gro'" or to fonn any contmuou, network. Th" change m mIcrostructure ",ith heal input i, al,o supported by the micro and macro hardncss values of these plate" A," resull the hardness value was the h'ghest al!he coarsesl and largest eutectic mixturcs. In each current setting there wa; dllullon of the eutectic mixture m the heat affected zone_ It was also ob,cncd lhal d,fferenee In hardness values between d,fferent portIOn, of lhe weld decreases a, lhe welding current tnereases becau", high heal input created more dllu(lOn in the weld structure, Agam when 5356 filler metal (Al-5%Mg) was u,ed for welding pure alUm1tllUmplales , another type of secondary phase was found during welding and it was Identified as globules of Mg,Al, precIpitates _H.re also the precipitate, were different m _,i"e, shape and orientation at d,fferent current setting, and at different locatlons of !he wel,lcd sample,_ In this ca,e ,olidifLcation eraekmg:appeared in the heat affected zone and m the weld portIOn,Here the tendency for this defect decreased)n the case when there was SUffj"l~'Ttlitme for solidificatLon after weldmg and when the temperature difference between the preClpilate, and the bulk matenal decreased, As a result whm welding condncted at the hLghest current setting the tendency for ,olldltkation cracking decreased, Another set of welding was performed usmg a base plate of5xxx series (AI-Mg alloy). Here (wo different current setting:of l45A and 175 A were used. In this case when 4043 filler metal WaS uscd for welding again Al-Si euteetic mixture formed but another phase of Mg,Si also fonned during weldmg. The eharactcri,tics of the eutectic mixture was the ,arne as the prCYlOlI'weldmg that ISat the highest current sclung the eutectic mixture was the large,t, coarsest and eontmuous m nature, However another phase of Mg,Si was also found and suspected to be responsIble for deteriorating the impact energy In thlS case the rnlcrohardnc" profiles exhibit that increase 1Il current content results in struc!uml homogeneity. FlIlally another base plate of 5~xx ,cries was welded at a current setting of] 75 A with 5356 (A1-Mg)filler melal and it need, funher studies to explalll the characteristics of this welded samples.