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The tensile properties,electrical conductivity,and microstructure of the forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy were investigated after a two-step ageing treatment at 120 and 170℃.The results indicate that the strength of the alloy reaches the peak value at 170℃ for 1 h during the second step ageing and then decreases sharply.However,the electrical conductivity value increases continuously with the second ageing time increasing.The fracture mechanism of the alloy is intergranular fracture for 1 h and then changes to dimple transgranular fracture later,and the toughness of the alloy is improved significantly.The phases of η’ and η are major precipitates in the alloy under the two-step ageing condition.Discontinuous grain boundary precipitates and precipitate-free zones along the grain boundary are clearly observed.
The tensile properties, electrical conductivity, and microstructure of the forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy were investigated after a two-step aging treatment at 120 and 170 ° C. The results indicate that the strength of the alloy reaches the peak value at 170 ° C. for 1 h during the second step aging and then decreases sharply. However, the electrical conductivity value increases continuously with the second aging time-increasing. The fracture mechanism of the alloy is intergranular fracture for 1 h and then changes to dimple transgranular fracture later, and the toughness of the alloy is improved significantly. the phases of η ’and η are major precipitates in the alloy under the two-step aging condition. Discontinuous grain boundary precipitates and precipitate-free zones along the grain boundary are clearly observed.