Reserch On Planar Solidification Of Pure Aluminum/7050 Aluminum Alloy And Heat Treatment Process Of 7050 Aluminum Alloy

Al-Zn-Mg-Cu as a super-high strength aluminum alloy with high specific strength,hardness,higher toughness,better corrosion resistance and mechanical performance is a key of light weight and high strength structural material applied in our nation's aviation,aerospace and ground vehicle.At present,the traditional DC casting method is used in preparing the AL-Zn-Mg-Cu ingots,however,with the high alloy content,it is quite difficult to make this kind of large-scale ingots with the tendency of macro segregation,cracking defects and low yield rates.This subject is based on "aluminum alloy planar solidification technology research" of the ministry of education priority development projects,it is carried on the basis of pilot experiments by improving and optimizing the planar solidification casting equipment,realizing the pure aluminum/7050 aluminum alloy planar solidification composite casting and significantly reducing the macro segregation of 7050 aluminum alloy in the casting process.The main results obtained are as follows:(1)Studying the speed of 7050 aluminum alloy liquid and the effects of the surface temperature(interface temperature)of pure aluminum on the compposite interface of pure aluminum/7050 aluminum alloy composite ingots in the casting process with the self designed planar solidification pilot experimental equipment.When the speed is 20mm/min(0.873 kg/min)and the pure aluminum surface temperature is around 600? in the casting processing of 7050 aluminum alloy,the interface is straight without crack,oxidation film,pores and so on,forming good metallurgical combination.(2)The good composite interface is required by conducting the large-scale(600mm×600mm×180mm)casting of composite ingots on the condition of applying the parameters determined by the pure aluminum/7050 aluminum alloy planar solidification casting pilot experiments.In the composite ingot casting of 7050 aluminum alloy,content of Zn?Mg and Cu three kinds of solute elements fluctuates slightly near average,and segregation rate is within 4%without significant macrosegregation and casting crack.Compared with DC casting,composite ingot casting reduces and eliminates macrosegregation obviously,achieving the goal of planar solidification homogenization of solutes;?-A1 are either equiaxed grain or equiaxed dendrite in 7050 aluminum alloy,and the grain sizes which are 290?310?m on each position in the ingots.(3)There are obvious dendritic segregation in 7050 aluminum alloy solidification structure with pure aluminum/7050 aluminum alloy composite ingots,grain boundary and dendritic dendrite gaps exist rich Zn,Mg and Cu with low melting point of non-equilibrium phases;Compared with the homogenization of 465?×48h,the residual phase proportion falls from 5.3%to 1.03%,and the dendritic segregation has been significantly improved.(4)The tensile strength is 366.67MPa,the elongation is 8.83%,the hardness and electrical conductivity are 115.7HV and 41.8IACS%,respectively in the rolling 7050 aluminum alloy of pure aluminum/7050 aluminum alloy composite ingots;the best solution process for 7050 aluminum alloy in the test range is at the holding temperature of 470? for 45 min and then quenching.at room temperature;By 95? × 2h+1 70? × 3 h+120? × 24h regression aging treatment,the alloy tensile strength is 585.92MPa,the elongation is 9.66%,the hardness and electrical conductivity are 149.3HV and 36.1IACS%,respectively.