Cutting Al-mg-si Alloys

Experimental techniques such as metallographic examination,mechanical property test,SEM and EDS were used to investigate the properties and microstructure of lead-free and free-cutting Al-Mg-Si alloy with the addition of Sn or Sn and Bi.And then machinability of the alloys were also studied by machinability experiments.The results show that:(1)Designed 4 alloys of group A based on conventional 6262 alloy,and Pb and Bi were replaced by Sn.The content of Sn in these alloys were 0.9%,1.1%,1.3% and 1.5%.The hardness of casting of these alloys are HB60.3,HB53.2,HB59.6 and HB45.1.And when the content of Sn was 1.3%,the machinability of the alloy was the best.So the optimum content of Sn to be added into lead-free and free-cutting 6061 alloy may be 1.3%.(2)After optimization of heat treatment of 1.3%Sn alloy,the best aging processing of lead-free and free-cutting Al-Mg-Si alloy after solution is 160℃×8h.And in this condition,the hardness of the alloy is Hb101.The machinability of the alloy after solution and aging is worse than casting,but with better surface.(3) Three alloys of group B were designed based on group A,and Bi was added into these alloys.The content of Sn in these alloys were 1.3%,and Bi were 0.4%,0.5% and 0.6%.The hardness of casting of these alloys are HB60.1,HB59.5 and HB51.9.And when the content of Bi was 0.5%,the machinability of the alloy was the best.So the optimum content of Bi to be added into lead-free and free-cutting Al-Mg-Si alloy may be 0.5%.(4)After optimization of heat treatment of 1.3%Sn and 0.5%Bi alloy,the best aging processing of lead-free and free-cutting Al-Mg-Si alloy after solution is 160℃×8h.And in this condition,the hardness of the alloy is HB98.3.The machinability of the alloy after solution and aging is as good as casting,but with better surface.(5)In this experiment,the hardness of casting of conventional 6262 free-cutting alloy is HB55.8.The content of 1.3%Sn alloy and the content of 1.3%Sn and 0.5%Bi alloy could replace the conventional 6262 free-cutting alloy.But the addition of Bi is better.(6)The alloy with 1.3%Sn and 0.5%Bi after solution and aging is better than 1.3%Sn only.(7)The technology principle of free-cutting aluminum alloy of Sn,Bi replace poisous Pb was that:in Al-Mg-Si alloy,low-melting tissue substance Mg2Sn and Sn,Mg3Bi2 and Bi were formed by Sn and Bi to ensure good machinability,and the synthesis mechanical property was insured by dispersion distributed Mg2Si precipitates.