Study On Heat Treatment Of The New Al-Mg-Si-Cu-Zr Alloy

This paper investigated the heat treatment of two new Al-Mg-Si,Cu-Zr alloy(The composition of alloy A is Al-1.55Mg-1.15Si-0.85Cu-0.11Zr,and the composition of alloy B is Al-1.25Mg-1.15Si-0.75Cu-0.14Zr-0.75Mn-0.03Sc),including homogenization,the solution treatment and the aging treatment.The differences of microstructures and mechanical properties of the extruded products after different heat treatments are investigated and the effect of Scandium and Manganese on microstructures and mechanical properties of Al-Mg-Si-Cu-Zr alloy is obtained by testing the mechanical properties and analyzing the microstructure,so as to find an excellent strength and toughness technical parameters of heat treatment.Through the research,we found that the two new Al-Mg-Si-Cu-Zr alloy cast ingot can be refined in DC casting.The percentage of residual phase of the alloy decreases with the increase of the average time,and the conductivity and the hardness increase with the increase of the time.When the alloy was homogenized at 560? for 24 hours,the non-equilibrium phases almost dissolves completely and the microstructures are more uniform.The conductivity of the alloy A can be improved from 35.50%IACS to 38.40%IACS and the alloy B can be improved from 28.80%IACS to 35.80%IACS.Scandium and Manganese added in the Al-Mg-Si-Cu-Zr alloy has an obvious influence on the microstructures and mechanical properties of the alloy after the extrusion and heat treatment.In the homogenization and aging process,lots of small and petal shaped Al3(Sc,Zr)phases precipited,which can inhibit recrystallization,refining grains and keeping fibrous microstructure after extrusion.In the process of solid solution treatment,with the increase of solid solution temperature,the strength of the alloy increases and the conductivity decreases,but increase in solid solution time has a little effect.The conductivity of the alloy decreased with the increase of time at first and then increased.The single stage aging tests were carried out at 150?,160?,170? and 180?,and the results show that the strength and conductivity of the alloy were the highest at 180?.The strength of the alloy increased with the increase of time at first and then tends to be stable.When the solid solution treatment at 560? for 2 hours and ageing at 180? for 24 hours,the alloy comprehensive performance is better.At this point,the RM,Re,A,hardness and conductivity of the alloy A were 392.50MPa,365.25MPa,16.00%,165.40,and 41.70%IACS respectively and the alloy B were 435.50MPa,398.50MPa,22.75%,172.90,and 43.40%IACS respectively.We found that relative importantce of four major factors in determinating the properties and conductivity of alloy A in two-stage aging treatment though a series of orthogonal experiment.The order was the final aging temperature T2>the final aging time t2>the pre-aging temperature T1>the pre-aging time t1.Relative importantce of four major factors in determinating the properties and conductivity of alloy B in two-stage aging treatment though a series of orthogonal experiment.The order was the final aging temperature T2>the pre-aging temperature T1>the final aging time t2>the pre-aging time ti.When the solid solution treatment at 560? for 2 hours and two-stage ageing at 160?for 6 hours at first and then at 185? for 16 hours,the alloy comprehensive performance is better.At this point,the Rm,Re,A,hardness and conductivity of the alloy A were 381.50MPa,366.00MPa,13.50%,148.20,and 43.30%IACS respectively and the alloy B were 428.50MPa,392.50MPa,10.25%,150.60,and 48.30%IACS respectively.