Effect Of Compacting Process Parameters And Heat Treatment Technology On Microstructure And Properties Of 6061 Aluminum Alloy

This thesis is based on the research subject 6061 aluminum alloy,taking the method of orthogonal test.The different effects on microstructure and mechanical properties of 6061aluminum alloy by technological parameter of compacting process were studied in this thesis.The best heat treatment process of 6061 aluminum alloy by the tensile test,SEM,DSC,TEM and other test methods was also explored in this thesis.It makes an analysis on the precipitation behavior and strengthening mechanism of 6061 aluminum alloy.Finally,the precipitation kinetics equation and the TTT expressions of β″phase are calculated in 6061 aluminum alloy.It shown that there are great significant influence on the grain sizes,which was made by specific pressure and mould preheating temperature in this thesis.With the increase of the specific pressure,the grain sizes varied from 81.903μm to 60.667μm.With the increase of the mould preheating temperature,the grain sizes varied from 60.667μm to 82.746μm.The specific pressure and the mold preheating temperature have the significant influence on the grain sizes,however,the pouring temperature and the dwell time have no obvious effects on the grain sizes.The influence of the factors on tensile strength in descending order is:specific pressure,mold preheating temperature,pouring temperature and dwell time.The effect of factors on elongation in descending order is:pouring temperature,preheating temperature of mould,dwell time and specific pressure.The casting tensile strength is 181.7MPa and the elongation is 15.4%,when the casting temperature is 720°C,the specific pressure is 150MPa,the pressure holding time is25s,and the preheating temperature of the mold is 150°C.There are five kinds of the component types for cast crystalline phases as follows:AlCuMgSi,MgSi,AlFeSi,AlMnFeSi and AlMnCrFeSi.There are also four structural types as follows:Al_1.9CuMg_4.1Si_3.3.3 phase,Mg₂Si phase,β-Al₅FeSi phase andα-Al₈Fe₂Si phase.In addition,Al₅FeSi phase,Al₅（MnFe）Si phase and Al₅（MnCrFe）Si phase are included inβ-Al₅FeSi phase,and Al₈Fe₂Si phase,Al₈（MnFe）₂Si phase and Al₈（MnCrFe）₂Si phase are included inα-Al₈Fe₂Si phase.With the changes of the parameters of solid solution time,aging temperature and aging time,the tensile strength,the yield strength and the hardness of the 6061 aluminum alloy will increase firstly and then decrease,consequently,the elongation will decrease firstly and then increase.The treatment process of T6 peak aging of 6061 aluminum alloy is as the follows:on the condition of 1 hour solution at 540°C,7 hours aging at 180°C.The tensile strength and yield strength are 314.7MPa and 304.3MPa respectively alloy,and the hardness and elongation are145.52HV and 10.8%respectively at T6 peak aging of 6061 aluminum.Processing hardening,fine grain strengthening,solid solution strengthening and second phase intensification can be used to improve mechanical properties of 6061 aluminum alloy.It will promote the precipitation of β″phase by the specific pressure of in 6061 al-uminum alloy.With the increase of specific pressure,the alloy β″phase activation energy is correspondingly decreased as the following:116.6,109.7,103.0kJ/mol.The kinetics expressions are obtained as follows:Y_0MPa=1-exp[-4.209×10¹⁶t^1.5exp（-21036.8/T）],Y_75MPa=1-exp[-2.892×10¹⁵t^1.5exp（-19791.9/T）]and Y_150MPa=1-exp[-2.187×10¹⁴t^1.5exp（-18583.1/T）].The TTT expressions are obtained as follows:T_0MPa=21036.8/[38.3+1.5lnt-lnln（1-Y）^-1],T_{75M Pa}=19791.9/[35.6+1.5lnt-lnln（1-Y）^-1]and T_150MPa=18583.1/[33.0+1.5lnt-lnln（1-Y）^-1].