Microstructure changes of Al-Zn-Mg-Cu 7075 aluminum alloy after single solution treatment,twice solution treatment and peak aging were investigated by means of optical microscope,X-ray diffractometer,scanning electron microscope and transmission electron microscope,and the effect of microstructure difference on intergranular corrosion sensitivity was analyzed.The results show that the composition uniformity of 7075 aluminum alloy increases and the intergranular corrosion sensitivity decreases significantly after twice solution treatment at 474 ℃ compared with single solution treatment.After peak aging,the grain boundary precipitates are chain-like,and precipitation-free precipitates appear on both sides,which hinders the formation of continuous corrosion channels.Cu enriched Mg(Zn,Cu)2 precipitates are formed at the grain boundary,and the corrosion potential difference with aluminum matrix is reduced,which improves resistance to intergranular corrosion of the material.The degree of supersaturated solid solution is increased in the twice solution treatment,which promoted the aging precipitation behavior.After the peak aging,the size and quantity of precipitated phase increase,and the spacing of the second phase at the grain boundary increases.The alloy shows better resistance to intergranular corrosion.
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