Effect Of Solidfication Conditions And Heat Treatment On The Microstructure And Properties Of Heat-resistant Al-Cu Alloy

This paper employs the low pressure casting method to prepare heat-resistant Al-Cu alloy barrel-shape sample.The heat treatment parameters was optimized by orthogonal experiment and the effects of different wall thickness and chill on the microstructure and mechanical properties of the alloy have been investigated.According to the results of orthogonal experiments,in the three heat treatments parameters,the aging temperature has the greatest influence on the properties of heatresistant Al-Cu alloy.Although the aging time has the least effect on the tensile strength of the alloy at room temperature,it has a great influence on the high temperature tensile strength of the alloy.The solution time has little effect on the high temperature properties of the alloy.Considering the comprehensive properties of the alloy,the optimum heat treatment parameters of the Al-5.0Cu-1.5Ni-0.35Mn-0.35Co-0.25Sb-0.22Ti-0.22 Zr alloy is determined as solution temperature of 535 ?+10h,aging temperature 190 ?+14h,and the quenching temperature is at 80?.The results show that the samples treated by the optimal heat treatment parameters have the highest value of the room temperature properties and high temperature properties,Tensile strength is 319.39 MPa,yield strength is 201.53 MPa,elongation is 8.52%;300 ? high temperature tensile strength is 151.19 MPa,yield strength is 129.03 MPa,elongation is 16.66%,which proves that the result of the orthogonal experiment is credible.The effects of different wall thickness on the microstructure and properties of the heat-resistant aluminum-copper alloy castings were studied.The results show that the percentage of the second phase in the alloy structure decreases with the increase of the wall thickness.And the second phase is unevenly distributed and the aggregation phenomenon is serious.The hardness,tensile strength and yield strength of the casting decrease with the increase of the wall thickness,but the elongation will be improved.After the heat treatment,the casting structure is improved.The tensile strength of the 20 mm castings is 271.55 MPa and the high temperature tensile strength at 300 ? is 136.30 MPa.The tensile strength of the castings is 286.46 MPa and the high temperature tensile strength at 300 ? is 138.92 MPa,both increased,room temperature elongation increased from 5.71% to 6.15%.The effect of different chill conditions on the microstructure and properties of heatresistant aluminum-copper alloy castings was studied.The results show that the use of chill can increases the cooling rate of castings,and the effect is more obvious than that of wall thickness.The use of chill can make the casting produce more second phase,and after heat treatment the second phase is more dispersed,the casting properties could be better.Contrasting as-cast microstructure and heat treatment state microstructure,the content of the second phase is obviously reduced after the heat treatment,part of which has been dissolved in the matrix,and the elements segregation is basically eliminated.The grain boundary after heat treatment is narrower than as-cast grain boundary,and it is discontinuous,but it is still distributed in the form of mesh or skeleton.The distribution is more diffuse;the grain after heat treatment is coarse.