双级峰时效对超高强Al-Zn-Mg-Cu合金微观组织与力学性能的影响

Effect of two-stage peak ageing on microstructure and mechanical properties of ultra-high strength Al-Zn-Mg Cu alloy

800 MPa级超高强Al-Zn-Mg-Cu合金对航空结构轻量化具有重要意义,但存在断裂伸长率波动较大的问题。本文提出了双级峰时效制度,系统对比了120℃单级时效、80℃一级时效和120℃二级时效处理后的微观组织和力学性能。结果发现:双级时效过程中,经一级时效处理后合金基体内析出了高密度的GP区,促进后续二级时效过程中晶内形成细小弥散的η′相,并减小了晶界无析出带宽度;二级时效时间在8−10 h之间时,合金强度最高且伸长率在10%以上。晶界无析出带宽度减小是伸长率提高的直接原因。

The ultra-high strength Al-Zn-Mg-Cu alloy of 800 MPa is of great significance to the lightweight of the aviation structure, but the fracture elongation fluctuates greatly at present. In this paper, a two-stage peak ageing process was proposed. The microstructures and mechanical properties of the alloys treated by single-stage ageing at 120 ℃, first-stage ageing at 80 ℃ and second-stage ageing at 120 ℃ were systematically compared. The results show that after the first-stage ageing treatment, high-density GP zones precipitate in the matrix, which promotes the formation of fine dispersion η′ phase during the second-stage ageing process. Compared with the single-stage ageing state, the width of precipitation free zone(PFZ) at grain boundary is reduced. When the second ageing time is between 8-10 h, the strength is the highest and the elongation is more than 10%. The decrease of the width of PFZ at grain boundary is the direct reason for the increase of elongation.