本文利用硬度,光学显微镜和透射电镜研究了微量Mn(0.48wt-%)对Al-5.0Zn-1.8Mg合金的沉淀过程,临界形核温度(T_C~′)和显微组织参数的影响,并与Cr和Cu的作用特点进行了比较.实验结果表明,Mn能细化晶粒和提高HV,但没有强烈的抑制再结晶和提高T_c~′的作用.在选用的时效条件下(120—200℃),含Mn合金的PFZ比无Mn合金窄,HV比无Mn合金高.在时效初期或进行低温时效(T_a≤160℃),Mn能促进晶界沉淀相(GBP)和基体沉淀相(MPt)的长大,但在时效后期或进行高温时效(Ta≥180℃),Mn又能抑制它们长大,有明显的稳定化作用.Mn对显微组织参数的这种影响与Cr和Cu的影响不同,可用Mn原子集团参与了GP区形核和含Mn之GP区的吞并长大速度慢的观点来说明.
The effect of 0.48 wt-% Mn,in contrast to Cr or Cu,on the precipitation,critical nucleation temperature,T_c′,and structural parameters of an Al-5.0wt-%Zn-1.8wt-%Mg alloy has been investigated by means of the hardness test,optical microscopy and TEM.It was resulted that the trace Mn addition may re-fine the grain size and increase the hardness,but can not vigorously inhibit the recrys-tallization and not raise T_c′.Under the selected aging condition at 120—200℃,thealloy containing Mn has narrower PFZ and higher HV than Mn-free one.Thetrace Mn may facilitate the growth of GBP and MPt during aging at initial stageor lower temperature≤160℃;however,it will be an obvious stabilizer to retardtheir growth during aging at final stage or elevated temperature≥180℃.Theabovemention to Mn,on the contrary to Cr or Cu,seems to be explained bythe supposition which the Mn cluster would participate the nucleation of GPzone thereafter slow down the rate of the coalescence and growth as well.
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