573K高溫時效處理的Al-10Mg合金中粗大β(Al3Mg2)相對熱壓縮組織演化的影響及機理

573K高溫時效處理的Al-10Mg合金中粗大β(Al3Mg2)相對熱壓縮組織演化的影響及機理EFFECT OF COARSE β (Al3Mg2) PHASE ON MICROSTRUCTURE EVOLUTION IN 573K ANNEALED AL-10MG ALLOY BY UNIAXIAL COMPRESSION

本文對高鎂Al-10Mg合金分別做了固溶與時效處理，固溶工藝為673K/24h，固溶后的高溫時效工藝為573K/24h，并對固溶及時效態試樣分別進行了兩道次壓縮試驗。通過OM、XRD、EPMA、EBSD等分析表征手段，研究了時效析出的β相對高鎂Al-10Mg合金熱變形過程中的力學性能及微觀組織演變的影響。結果表明，時效處理后晶粒內部析出了均勻分布的β相，兩道次壓縮試驗后時效態試樣的應力-應變曲線始終處于固溶態試樣曲線的下方。第一道次壓縮試驗中時效態試樣的硬化率低于固溶態試樣的硬化率，在回復過程中固溶鎂原子對形變強化起主要作用，第二道次壓縮試驗中時效態試樣的硬化率高于固溶態試樣的硬化率、時效態試樣內部的位錯累積更顯著并且更早地出現了再結晶軟化。時效態試樣壓縮組織內殘余了更多的形變儲能，使β相激發出更多的小角度晶界、進而將變形晶?；w切割成若干區塊，因此促進了再結晶形核從而細化了再結晶晶粒。再結晶形核不再局限于晶界凸出（Bulging）形核，再結晶晶粒不再具備典型的再結晶織構特性，各向異性被弱化。β相阻礙了位錯的滑移，將部分變形儲能累積在沉淀相周圍的小角度晶界處，減少了滑移到變形晶粒晶界處的位錯數量，從而減緩了變形晶粒晶格的旋轉，使變形晶粒含有{001}和{101}兩種面織構組分。

Al-Mg series alloy plays an important role in offshore manufacturing, transportation and aerospace industries for its high strength-to-weight ratio, high corrosion resistance and good welding performance. For high Magnesium Al-Mg alloy, β phase always acts as a restraint condition to the whole thermal mechanical processing (TMS) procedure. Its positive effect is still unclear. In this paper, 573K/24h annealed Al-10Mg alloy was selected to study the effect of coarse β (Al3Mg2) phase on microstructure evolution. X-ray Diffraction (XRD), Electron Probe Micro-analyzer (EPMA), Electron Backscattered Diffraction (EBSD) characterization and double passes uniaxial compression were applied. The result shows that discrete coarse β phase precipitated in the interior of grains after 573K/24h annealing treatment. The true stress-true strain curve of annealed sample was lower than that of solution treated one. Hardening rate of annealed sample was lower in first compression pass, and conversely higher than solution treated one in the second pass. Solution Mg atoms played an important role in strain hardening during dynamic recovery. Dislocation slipping was obstructed by coarse β phase, and then low angle boundary (PLAB) was stimulated near coarse β phase. Not just bulging nucleation mechanism working, dynamic recrystallization nucleation was stimulated and microstructure was refined. Since part of deformation-stored energy was lured away by PLAB, lattice rotation of deformed grains were weakened possessing {001} and {101} simultaneously. Schmid factor of three blocks with different lattice orientation were calculated, which suggested that alloy can load more plastic deformation after annealing treatment. Not just bulging nucleation mechanism working, texture of recrystallized new grains was weakened at the same time. Microstructure anisotropy could be controlled by coarse β phase in TMS.

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