The Effect Of Sn Or In Addition On Natural Aging And Artificial Aging Of Al-Mg-Si Alloys

Due to its excellent mechanical properties,stamping formability and corrosion resistance,the 6000-series aluminum alloy has become the main lightweight material for automotive body panels.After quenching,6000-series aluminum alloys are stored at room temperature and thus natural aging will happen.which will generally have a negative effect on subsequent bake hardening and artificial aging.At present,the industrial use of pre-aging treatment is to inhibit the generation of natural aging,and alloying design is also an important way.Although Sn and In have low solid solubility in Al matrix,both of them have greater binding capacity to vacancies,and the formation of solute-vacancy pairs can effectively inhibit natural aging.Therefore,the contrast of the effects of Sn and In addition on the natural aging and artificial aging of Al-Mg-Si alloys is necessary.In this thesis,three kinds of Al-Mg-Si alloys were designed.Alloy 1 was the basic alloy,alloy 2 and alloy 3 were respectively added with 0.1 wt.%of Sn or In,respectively.The microstructure of the alloy was characterized by SEM,EDS,EBSD and TEM.The variation of mechanical property and electrical conductivity were obtained by microhardness test and electrical conductivity test during natural aging and artificial aging.DSC was used to analyze the effects of Sn,In and natural aging on the precipitation kinetics of the alloy.The main conclusions are as follows:?1?Sn and In had no significant effect on the texture and grain size of the alloy after solution treatment.The main texture types of the three alloys were recrystallized textures,and the content of Cube_ND and R texture was relatively high..?2?Sn and In had a significant inhibition on the natural aging of the alloy,especially at the initial stage of natural aging.After two weeks of natural aging,the hardness of Sn-added alloy and In-added alloy was still lower than that of the base alloy,and the electrical conductivity was higher than that of the base alloy.?3?DSC analysis showed that both Sn and In shifted the exothermic peak of the??phase to the high temperature direction,but In made the exothermic peak of the??phase gentler and the peak area larger.Although In slowed the time at which the??phase started to precipitate,In promoted more??phases precipitation.In addition,the natural aging also shifted the exothermic peak of the??phase to high temperatures,indicating that natural aging had a negative effect on subsequent artificial aging.?4?Sn made the??phase coarse and sparsely distributed,leading to the decrease of the peak age harness of the alloy 2.But In made the??phase fine and densely distributed,causing to the increase of the peak-aged hardness of the alloy 3.?5?Temperature had an important effect on artificial aging.Compared with the artificial aging at 170 ^? and 180 ^?,when it was at 200 ^?,the hardening rate of the alloy was significantly increased,and the time required for peak aging was shortened from 6 hours to 2 hours.However,high temperatures caused a significant coarsening of the??phase.