工艺参数对7075半固态铸-锻组织均匀性的影响
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摘要
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.
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.
引文
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[2]MLLER H,CURLE U A,MASUKU E P.Characterization of surface liquid segregation in SSM-HPDC aluminium alloys 7075,2024,6082and A201[J].Transactions of Nonferrous Metals Society of China,2010,20(3):847-851.
[3]GOVENDER G,MLLER H.Evaluation of surface chemical segregation of semi-solid metal cast aluminium alloy A356[J].Solid State Phenomena,2008,751(141):433-438.
[4]WANG S C,LI Y Y,CHEN W P.Microstructure evolution of semi-solid 2024alloy during two-step repeating process[J].Transactions of Nonferrous Metals Society of China,2008,18(4):784-788.
[5]SEO P K,KIM D U,KANG C G.The effect of the gate shape on the microstructural characteristic of the grain size of Al-Si alloy in the semi-solid die casting process[J].Materials Science and Engineering:A,2007,445/446:20-30.
[6]肖文华.半固态5083铝合金压缩行为及触变轧制研究[D].广州:华南理工大学,2011.XIAO Wenhua.Study on Compression Behavior and Thixo-Rolling of Semi-Solid 5083Aluminum Alloy[D].Guangzhou:South China University of Technology,2011.
[7]钱福梅.2024铝合金半固态触变模锻过程研究及数值模拟[D].哈尔滨:哈尔滨工业大学,2011.QIAN Fumei.Research on the Semi-Solid Thixoforging Process and Numerical Simulation of Aluminum Alloy 2024[D].Harbin:Harbin Institute of Technology,2011.
[8]DU Z M,CHEN G,CHENG Y S,et al.Inhomogeneity of density and mechanical properties of A357aluminum alloy backward extruded in semi-solid state[J].Transactions of Nonferrous Metals Society of China,2011,21(10):2285-2293.
[9]陈刚.2A50铝合金半固态模锻成形的组织性能不均匀性研究[D].哈尔滨:哈尔滨工业大学,2009.CHEN Gang.Research on Inhomogeneity of Microstructure and Mechanical Properties for 2A50Aluminum Alloy Prepared by Thixoforging[D].Harbin:Harbin Institute of Technology,2009.
[10]谭建波,王子超,王东旭.杯形件半固态模锻充型过程模拟及实验验证[J].河北科技大学学报,2015,36(3):313-318.TAN Jianbo,WANG Zichao,WANG Dongxu.The simulation and verification of the filling process of cup shell semi-solid die forging[J].Hebei University of Science and Technology,2015,36(3):313-318.
[11]VIEIRA E,FERRANTE M.Prediction of rheological behaviour and segregation susceptibility of semi-solid aluminium-silicon alloys by a simple back extrusion test[J].Acta Materialia,2005,53(20):5379-5386.
[12]秦晋.铝合金T型件半固态填充-塑性流动一体化模锻研究[D].哈尔滨:哈尔滨工业大学,2010.QIN Jin.Investigation of T-Shaped Workpiece Semi-Solid Aluminum Alloy Filling-Plastic Flowing inThixoforging[D].Harbin:Harbin Institute of Technology,2010.
[13]LIU D,ATKINSON H V,KAPRANOS P,et al.Effect of heat treatment on structure and properties of thixoformed wrought alloy 2024[C]//Proceedings of the 7th International Conference on Semi-Solid Processing of Alloys and Composites.[S.l.]:[s.n.],2002:311-316.
[14]谭建波,杨帅,李祎超.半固态6061合金流变铸-锻成形及组织均匀性[J].特种铸造及有色合金,2015,35(6):561-565.TAN Jianbo,YANG Shuai,LI Yichao.Research on forming process and microstructure uniformity of semi-solid rheological casting-forging6061alloy[J].Special Casting&Nonferrous Alloys,2015,35(6):561-565.
[15]王顺成,戚文军,郑开宏.半固态模锻ZL101铝合金车轮的组织与力学性能[J].材料热处理学报,2013,34(5):116-120.WANG Shuncheng,QI Wenjun,ZHENG Kaihong.Microstructureand mechanical properties of semisolid forged ZL101aluminum alloy wheel[J].Transactions of Materials and Heat Treatment,2013,34(5):116-120.
[16]谭建波,杨帅,李祎超.工艺参数对半固态流变铸-锻6061合金成形性的影响[J].河北科技大学学报,2016,37(1):65-69.TAN Jianbo,YANG Shuai,LI Yichao.Effect of technological parameters on formability of semi-solid rheological casting-forging 6061alloy[J].Journal of Hebei University of Science and Technology,2016,37(1):65-69.
[17]王子超,谭建波.铝合金半固态模锻技术研究现状[J].铸造设备与工艺,2016(1):54-58.WANG Zichao,TAN Jianbo.Research status of aluminum alloy semisolid die forging technology[J].Foundry Equipment and Technology,2016(1):54-58.
[18]KAPRANOS P,LIU T Y,ATKINSON H V,et al.Investigation into the rapid compression of semi-solid alloys slugs[J].Journal of Materials Processing Technology,2001,111(1/2/3):31-36.
[19]FLEMINGS M C.Behavior of metal alloys in the semi-solid state[J].Metallurgical Materials Transactions A,1991,22(5):957-981.
[20]JOLY P A,MEHRABIAN R.The rheology of a partially solid alloy[J].Journal of Materials Science,1976,11(8):1393-1418.