Cr、Mn、Zr、Ti微合金化对Al-Zn-Mg-Cu-Yb合金再结晶、第二相和断裂行为的影响

Effect of Minor Cr, Mn, Zr or Ti on Recrystallization,SSecondary Phases and Fracture Behaviour of Al-Zn-Mg-Cu-Yb Alloys

摘要:

采用拉伸测试,结合XRD、TEM、SEM和EBSD等物相和微观结构表征,研究了单独添加Cr、Mn、Zr、Ti对Al-Zn-Mg-Cu-Yb合金第二相(特别是AlCuYb相)析出、基体再结晶行为和拉伸沿晶断裂的影响。研究结果表明：在同时添加Yb和Cu的铝合金中,微米级、粗大AlCuYb相的析出难以避免。但有趣的是,进一步添加Mn的合金中,由于析出了亚微米的Al₂₀Cu₂Mn₃相,可有效减少粗大AlCuYb相,在四种合金中形成的粗大相的数量最少。Al-Zn-Mg-Cu-Yb合金中添加Zr,可析出纳米级 Al₃(Yb, Zr)弥散相,有效抑制结晶,但是AlCuYb相的形成消耗Yb元素,降低了二次共格Al₃(Yb, Zr)弥散相的析出,此外粗大AlCuYb相颗粒诱发局部再结晶,一定程度降低了合金的强度。T6态 Al-Zn-Mg-Cu-Yb-Zr和Al-Zn-Mg-Cu-Yb-Mn合金经固溶后仍保持未再结晶纤维状结构,小角度再结晶分数高达50%以上,平均晶粒尺寸降至2~7 μm。相比之下,添加Cr或Ti的Al-Zn-Mg-Cu-Yb合金形成的均匀的再结晶晶粒,大角度再结晶分数高达80%,平均晶粒尺寸为40-96 μm。断裂时,尺寸1~3 μm的初生Al₂CuMg相(而非粗大AlCuYb相)优先诱发断裂,裂纹沿析出相连续、粗大且无沉淀析出相宽化的大角度再结晶晶界或原始晶界扩展。

关键词:铝合金; 二次相; 再结晶; 稀土元素; 断裂行为

Abstract:

The effects of sole Cr, Mn, Zr, Ti addition on the precipitation of secondary phases (especially AlCuYb), matrix recrystallization behaviour and tensile intergranular fracture of an AlZnMgCuYb based alloy has been investigated by using tensile test, together with detailed microstructural characterization XRD, TEM, SEM, and EBSD technique. The results indicate that coarse micro-scaled AlCuYb phase precipitated can not be inevitable in the Yb and Cu containing Al alloy. It is interesting that the least coarsen phases are formed in the AlZnMgCuYb-Mn alloy due to the precipitation of submicro-scaled Al₂₀Cu₂Mn₃ phase resulting in the effective decreasing of coarse AlCuYb phases. The addition of Zr to AlZnMgCuYb alloy can effectively inhibit the recrystallization of ɑ(Al) matrix by the formation of nano-scale coherent Al₃(Yb, Zr) dispersoids. However, the formation of AlCuYb phases consuming Yb will reduce secondary coherent Al₃(Yb, Zr) precipitation and particleSstimulated partial recrystallization nucleation, resulting in a decline in strength of AlZnMgCuYb-Zr alloy. T6-tempered AlZnMgCuYb-Zr and AlZnMgCuYb-Mn alloys still remain an unrecrystallized fiber-like structure, the fraction of low-angle grain boundaries (LAGBs) increased up to 50%, and the average grain size decreased to 2~7 μm. However, more homogeneous recrystallization grains are observed in Cr or Ti containing AlZnMgCuYb alloy, the fraction of high-angle grain boundaries (HAGBs) and the average grain size achieve 80% and 40-96 μm, respectively. The primary 1~3 μm Al₂CuMg particles, not coarse AlCuYb preferentially cracked, and cracking propagated along high-angle recrystallized grain boundaries or original grain boundaries with continuous, coarser grain boundary precipitates and broadening precipitate-freeSzones (PFZs) at its periphery.

Key words:aluminium alloys; secondary phases; recrystallization; rare earth element; fracture behaviour