Al-Zn-Mg-Cu合金厚板沿厚度方向的显微组织和硬度

Microstructure and hardness of Al-Zn-Mg-Cu alloy thick plate along thickness direction

利用金相显微镜、场发射扫描电镜、透射电镜和硬度计研究了7050-T7451铝合金厚板沿厚度方向的显微组织、再结晶、第二相、时效析出相和无沉淀析出带,以及显微硬度的演变。结果表明:80mm厚7050铝合金厚板在热处理过程中发生不同程度的再结晶,从表层到心部再结晶晶粒平均尺寸和面积分数沿厚度方向呈现出先降低后增加的趋势,并且各厚度层的再结晶面积分数均小于5%,而第二相平均尺寸逐渐增大,面积分数在表层较小而心部相对较大;晶内析出相密度在各厚度层基本无差异,但晶界析出相在心部比其他厚度层的更断续,尺寸更大,而表层则间距和尺寸更小。此外,在不同厚度层均存在明显的无沉淀析出带,并且其宽度随晶界析出相大小而变化,心部无沉淀析出带宽度较宽,约为94nm。各厚度层的显微硬度值从表层到心部呈现出先增大后减小趋势,并与再结晶程度和亚稳态η`相有关。

Evolution of the metallographic structure,recrystallization,second phase,aging precipitated phase,precipitation free zone and microhardness of the 7050-T7451 aluminum alloy thick plate with different thickness layers along the thickness direction were studied by means of metallographic microscopy,field emission scanning electron microscopy,transmission electron microscopy and hardness meter.The results show that the 80 mm thick 7050 aluminum alloy plate has different degrees of recrystallization during heat treatment.The average grain size and area fraction of recrystallization from the surface to the center show a trend of first decreasing and then increasing along the thickness direction,and the recrystallization area fraction of each thickness layer is less than 5%,while the average size of second phase increases gradually,the area fraction is smaller in the surface layer and relatively larger in the center.The density of intragranular precipitates is basically consistent in each thickness layer,but the precipitates at grain boundaries are more discontinuous and larger in size in the center compared to other thickness layers,while the spacing and size of the surface layer are smaller.In addition,there are obvious precipitate free zones(PFZ)in different thickness layers,and their widths vary with the size of precipitates at grain boundaries.The width of the precipitate free zone in the center is relatively wide,about 94 nm.The hardness values of each thickness layer show a trend of first increasing and then decreasing from the surface to the center,and are related to the degree of recrystallization and metastableη`phase.