Pre-aging And Micro-alloying Study Auto Body 6022 Alloy Microstructure And Properties

In this paper, the alloy composition has been optimized on basis of 6022 alloy and four aluminum alloys were prepared.The effect of homogenization treatment, pre-aging treatment, addition of Ag and Sc+Zr has been investigated using Microscope, Transmission Electron Microscope(TEM), Scanning Electron Microscope(SEM), Differential Scanning Caborimetry(DSC), micro-hardness measurement, tensile test and formability test.Obtained these conclusions as follows:(1)It has been found that large quantity of constituents phases in 6022 alloy as cast condition. Constituents phases could dissolute fully after homogenization treatment of 540℃×32h and the arborescent structure could vanish.6022 alloy has a better paint-bake aging property and formability than the applied alloy sheet.(2)It was indicated that Mg-Si Clusters'dissolution process of the nature-aging alloys in the early stages of artificial aging reduce the alloy's mechanical properties and hardness. Mg-Si Clusters formed after pre-aging treatment which can serve as nucleation sites for theβ" in the subsequent artificial aging, result the increment of hardness and mechanical properties.(3)It was found that, with the pre-aging time increased, the formability of alloys was declined, while the mechanical properties was promoted. Pre-aging at 80℃for 10min, the formability of alloys declined small,but the increase of mechanical properties was also small.The Superior formability and mechanical properties was obtained pre-aging at 140℃for 10min.(4)It was found that the formability of 6022 alloy containing 0.35%Ag (after 5days nature aging) was declined with a liitle amount, and after 30 minutes paint-bake aging at 175℃higher strength could be obtained(σ0.2increase 30Mpa,σb increase 29Mpa).Ag addition also could improve the aging response and hardness. It also revealed that Ag addition could promote the formation of the theβ" phase which should prefer to nucleate on the position of G.P.zones/Clusters.(5)It was found that the formability of 6022 alloy containing 0.12Sc +0.13Zr (after 5days nature aging) was declined with a liitle amount, and after 30 minutes paint-bake aging at 175℃higher strength could be obtained(σ0.2increase 26Mpa,σb increase 23Mpa).The main reason was that lots of Al3Sc and Al3Zr formation in the process of homogenization treatment and solution treatment.But these phases do not influence the main pricipitationg process of alloys.