Er微合金化對2055鋁鋰合金力學(xué)性能及微觀組織的影響

Er微合金化對2055鋁鋰合金力學(xué)性能及微觀組織的影響EFFECT OF Er MICRO-ALLOYING ON MECHANICAL PROPRTIES AND MICROSTRUCTURES OF 2055 Al-Li ALLOY

研究了0.2%及0.4%Er的添加對2055 Al-Li合金T8態(tài)時(shí)效 (6%預(yù)變形+160℃時(shí)效)微觀組織和力學(xué)性能的影響. 結(jié)果表明, 0.2%Er添加顯著降低合金強(qiáng)度, 但延伸率略有增加. 微量 Er 添加未改變 Al-Li 合金中時(shí)效析出相的種類, 主要強(qiáng)化相仍然為 T1 相 (Al2CuLi)及θ′相 (Al2Cu), 但時(shí)效析出相的數(shù)量明顯減少, 同時(shí)時(shí)效析出的響應(yīng)速度減緩. 2055 Al-Li 合金中添加微量Er, 凝固時(shí)可形成Al8Cu4Er 相粒子, 這些粒子在后續(xù)均勻化及固溶處理時(shí)均難以完全溶解至固溶體中, 導(dǎo)致固溶基體中Cu 含量降低, 因而時(shí)效時(shí)含Cu 析出相T1 相及θ′相含量減少, 合金強(qiáng)度降低.

Al-Li alloys are considered as the ideal structural materials for aerospace industry because of its 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 was 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% 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 showed 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 T1 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.

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