Journal of Hebei University of Science and Technology (Apr 2017)
Influence of process parameters on the uniformity of microstructure of semi-solid casting-forging 7075 alloy
Abstract
Liquid phase segregation frequently occurs in the process of semi-solid die forging, which makes the parts appear “weak point” or “weak region”, and usually, the “weak point” or “weak area” is the reason of crack and service condition failure. In order to analyze the influencing factors for the liquid phase segregation of the semi-solid die forging, in this paper, the sample of semi-solid 7075 alloy is prepared by hand stirring method. The casting-forging forming of the sample is made by means of press machine and cup mould to research the influence of alloy temperature, head preheating temperature, hold time and other process parameters on the uniformity of the microstructure. The results show that the semi-solid casting-forging process is feasible within a set of mold. Under the conditions of head temperature of 400 ℃, hold time of 2 s and the forming pressure of 50 MPa, the liquid phase segregation degree of cup sample increases, the uniformity of the microstructure becomes worse with increasing of alloy temperature. The segregation degree is up to 14.02% when the alloy temperature is 628 ℃. The liquid phase segregation degree of cup sample decreases and uniformity of the microstructure becomes better along with increasing of head preheating temperature. Under the conditions of alloy temperature of 621 ℃, the forming pressure of 50 MPa, and head preheating temperature of 400 ℃, the liquid phase segregation degree of cup sample decreases, the uniformity of the microstructure becomes better along with increasing of the hold time. The segregation degree is up to 2.99% when the hold time is 4 s. The results could provide theoretical reference for the process formulation and experimental research of aluminum alloy semi-solid casting-forging forming.
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