Study On Semisolid Thixoforging Technology Of 7085 Alloy

A die forged part with 500MPa rank will be developed in this work for meeting the need of lightweight of tanks.High strength 7085Al alloy was used in semisolid thixoforging.Effects of the DC casting methods for semisolid ingots,temperature and time of second heating,temperature of thixoforging,ratio of height and diameter of the blank,temperature of die and heat treatment of the parts forged on microstructure and properties of the forged parts were studied in this paper to provide theoretic and technic basics for production in large-scale.The main results are as followings:(1)The microstructure of ingots cast by common DC casting is dendritic grains whose size is large.The grain became finer and into rosiness or nearly ball when the ingots DC cast with low frequency electromagnetic field.The grains of the ingots DC cast at liquidus temperature are near ball and finer than that by common DC casting.Application of low frequency electromagnetic field has a little effect on the grain size and shape in the ingots DC cast at liquidus.(2)During second heating the large the grain size,the high the temperature at same holding time,and the large the grain size,the longer the holding time at same temperature.Increase temperature and holding time will facilitate spheroidizing of grains.(3)Higher mechanical properties of the forged parts were achieved when the parts were forged at 590℃～600℃ and T6 treatment.The strength of the parts forged by the ingots DC cast at liquidus is 535MPa～547MPa and its elongation is 16-17%.The strength of the parts forged by the ingots DC cast at liquidus with low frequency electromagnetic field is 512MPa～532MPa and its elongation is 17-18%.(4)Temperature of the die has great effect on microstructure and mechanical properties of the forged parts.The parts forged when the temperature of the die is 200℃ have lower mechanical properties because the temperature decrease of the parts is very fast.The better results can be obtained when the parts forged at 300℃～400℃ and T6 treatment at which the strength of the parts forged by ingots DC cast at liquidus is 505MPa～533MPa,and its elongation is 5-15%,the strength of the parts forged by ingots DC cast at liquidus with low frequency electromagnetic field is 514MPa～532MPa,and its elongation is 10-17%.(5)Ratio of height and diameter of the blank is an important parameter for semisolid thixoforging.The fractures are formed in the parts easily at high ratio,which will reduce the mechanical properties of the parts.When ratio is 0.47-0.93 the strength of the parts forged by ingots DC cast at liquidus is 519MPa～533MPa,and its elongation is 18-20%,the strength of the parts forged by ingots DC cast at liquidus with low frequency electromagnetic field is 479MPa～532MPa,and its elongation is 17-20%.(6)The mechanical properties of the parts treated by T6 is high than that by T5 because the residual non-equilibrium eutectic can not be dissolved fully,which decreases the strength and plasticity of the parts markedly.(7)The adaptive forge reduction of 7085 alloy in thixoforging is 63～73%at which the strength of the parts forged by ingots DC cast at liquidus is 519MPa～533MPa,and its elongation is 16-19%,the strength of the parts forged by ingots DC cast at liquidus with low frequency electromagnetic field is 475MPa～532MPa,and its elongation is 12-20%.