Er微合金化对2055 Al-Li合金微观组织及力学性能的影响

EFFECT OF Er MICRO-ALLOYING ON MECHANICAL PROPERTIES AND MICROSTRUCTURES OF 2055 Al-Li ALLOY

研究了0.2%及0.4%Er的添加对2055 Al-Li合金T8态时效(6%预变形+160℃时效)微观组织和力学性能的影响.结果表明,0.2%Er添加显著降低合金强度,但延伸率略有增加.微量Er添加未改变Al-Li合金中时效析出相的种类,主要强化相仍然为T1相(Al2Cu Li)及q'相(Al2Cu),但时效析出相的数量明显减少,同时时效析出的响应速度减缓.2055 Al-Li合金中添加微量Er,凝固时可形成Al8Cu4Er相粒子,这些粒子在后续均匀化及固溶处理时均难以完全溶解至固溶体中,导致固溶基体中Cu含量降低,因而时效时含Cu析出相T1相及q'相含量减少,合金强度降低.

Al-Li alloys are considered as the ideal structural materials for aerospace industry because of their low density, high specific strength and specific elastic modulus as well as low fatigue crack growth rate and good low temperature performance. 2055 Al-Li alloy among new Al-Li alloys developed recently is a super-high strength Al-Li alloy. An important method to improve the performance of Al-Li alloys is to add micro-alloying elements. Er-microalloying in Al alloy has been investigated much, but the study on Al-Li alloy is still seldom reported. In this work, the effect of 0.2%Er and 0.4%Er addition on the microstructure and mechanical properties of 2055 Al-Li alloy sheet with T8 aging （6% cold rolling pre-deformation and aging at 160 ℃） were investigated. The results show that the addition of 0.2% Er significantly decreases the strength by about 50 MPa, but enhances the elongation; the strength is further decreased by about 100 MPa with the addition of 0.4%Er. The precipitate types in Er micro-alloyed Al-Li alloy are not changed with the addition of Er, and the aging precipitates are still T1 （Al2CuLi） and θ＇ （Al2Cu） phases. In the Er-microalloyed Al-Li alloy, the incubation time of T1 precipitate is longer, and its precipitation rate is decreased, accordingly the aging response is slowed. Meanwhile, under peak-aging condition, the fraction of T 1 precipitates, especially θ＇ precipitates in the Er-microalloyed Al-Li alloy is decreased, which results in a decrease of strength. As Er is added to the Al-Li alloy, Er-contained particles Al8Cu4Er are formed during solidification process, and their amount is increased with the addition increasing. These particles cannot be completely dissolved into the alloy matrix during homogenization process. After solution treatment following cold rolling, they are not yet dissolved into the solid solution. These particles contain Cu and Er simultaneously, and the concentration of dissolved Cu in solid solution is therefore decreased, With increasing Er addition, the Cu concentration in solid solution is further decreased. The precipitation rate of T1 is consequently decreased, slowing the aging response of the Er-microalloyed Al-Li alloy. And this factor also decreases the fraction of T1 and θ＇ precipitates and lowers the alloy strength.