工艺参数对7075半固态铸-锻组织均匀性的影响

Influence of process parameters on the uniformity of microstructure of semi-solid casting-forging 7075 alloy

在半固态模锻过程中,经常会出现液相偏析现象,使零件中出现"弱点"或"弱区",这些"弱点"或"弱区"通常又是潜在的裂纹源和服役条件下失效的起因。为了分析研究半固态模锻液相偏析的影响因素,采用手工搅拌法制备半固态7075合金,利用压力机及杯形实验模具,进行7075半固态铸-锻成形,研究了合金温度、压头预热温度、保持时间等工艺参数对7075半固态铸-锻组织均匀性的影响。结果表明:在一套模具内实现铸造和锻造是可行的;在压头预热温度为400℃,保持时间为2s,成形比压为50MPa的条件下,随着合金温度的增加,杯形件的液相偏析度增加,组织越不均匀,当合金温度为628℃时,杯形件的液相偏析度为14.02%;随着压头预热温度的增加,杯形件的液相偏析度减小,组织越均匀;在合金温度为621℃,成形比压为50MPa,压头预热温度为400℃时,随着保持时间的增加,杯形件的液相偏析度减小,组织越均匀,当保持时间为4s时,杯形件的液相偏析度为2.99%。该结果可为铝合金半固态铸-锻成形工艺的制定和相关研究提供理论参考。

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 2sand the formingpressure 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 4s.The results could provide theoretical reference for the process formulation and experimental research of aluminum alloy semi-solid casting-forging forming.