Study Of Heat Treatment Process And Microstructure And Performance Of Al-Mg-Si-Cu-(Li) Alloy

Since Al-Mg-Si-Cu-(Li)alloy has good processability,it can obtain a good strengthening effect after heat treatment process.In order to further improve the properties of the alloy,this experiment first studied the effects of the addition of different Li contents and La,Ce,B on the microstructure and properties in the Al-Mg-Si-Cu-(Li)alloy.The effects of La,Ce,and B in the alloy and the optimal Li content were investigated by exploring the optimal solution and aging regime and by analyzing the microstructure and properties of as-cast,homogenized,cold-rolled,and aging alloys.Based on this,the step ageing process of Al-Mg-Si-Cu-(Li)alloys without Li and with optimal Li content and the effects of natural parking on the step ageing process were studied.In the as-cast Al-Mg-Si-Cu-(Li)alloy,as the Li content increases,the dendrite grain boundaries become inconspicuous,there are more spherical and stripe phases,the hardness increases continuously,and the conductivity decreases continuously.Adding La,Ce,B can reduce the spherical phase,and at the same time,the continuity of the phase boundary is strengthened.The hardness is higher than without addition,and the conductivity decreases.After the as-cast alloy of each component is homogenized,the strip-like phase basically disappears and dissolves into the matrix.As the Li content increases,the hardness of the alloy increases continuously,and the electrical conductivity decreases continuously.Addition of La,Ce,and B increases the hardness and decreases the electrical conductivity.Compared with the as-cast alloy,the hardness is greatly reduced and the electrical conductivity is greatly increased after homogenization.In the cold-rolled state,as the Li content increases,the fiber structure of Al-Mg-Si-Cu-(Li)alloy is refined.Plus,with the addition of 0.15wt%B,the fiber structure is also refined and uniform.Determined by variation the temperature and time,the optimal solution process of Al-Mg-Si-Cu-(Li)alloy is 530?×1h,and the optimal aging process is 170? ×4h.As the Li content increases,the amplitude of the peak hardness increases from the start and then decreases later,and the conductivity decreases generally.Peak hardness is relatively close when adding La,Ce,B after aging.Stretching at the optimal solid solution and aging process,it was found that as the Li content of the alloy increases,the yield strength and tensile strength increase at first and then decrease later,and the yield strength and tensile strength of the alloy reach the highest value when Li is 0.1 wt%.However,the elongation gradually decreased with the increase of Li content.Scanning the fracture revealed that the number of dimples decreased and the brittleness increased.Added La,Ce,and B,yield strengths of Al-Mg-Si-Cu-(Li)increased by 25MPa,21 MPa,and 17MPa respectively,and the tensile strength did not increase much.A step aging process for Al-Mg-Si-Cu-(Li)alloy has developed at 170 ? for 5 minutes and 60 minutes pre-aging plus 30 minutes final aging.The performance of the graded aging process is close to or even better than single-stage aging.The effect of 5 minutes pre-aging plus 30 minutes of final aging enhancement is obvious.Pre-aging of 5,60 minutes after natural parking does not have a big negative impact on the final aging process,but yield and tensile strength have been improved.