中間退火對2A97鋁鋰合金晶粒細(xì)化及超塑性的影響Effects of intermediate annealing on grain refinement and superplasticity of 2A97 aluminum-lithium alloy

采用形變熱處理法制備2A97鋁鋰合金細(xì)晶板材，利用光學(xué)顯微鏡、透射電鏡和高溫拉伸等試驗(yàn)方法研究中間退火溫度對板材晶粒細(xì)化和超塑性的影響。結(jié)果表明：板材在室溫軋制時(shí)，當(dāng)變形量達(dá)到22%時(shí)，出現(xiàn)開裂，隨著軋制溫度的升高，開裂程度逐步緩解；將開軋溫度提高到400 ℃、軋制變形量達(dá)到88%時(shí)，分別在240、300和400 ℃進(jìn)行中間退火1 h，可解決開裂問題。但退火溫度對超塑性伸長率有很大影響，當(dāng)退火溫度為400 ℃時(shí)，合金發(fā)生了明顯部分再結(jié)晶，位錯(cuò)密度大幅降低，雖獲得總變形量為92%的無開裂板材，由于較多的形變儲(chǔ)能被釋放，晶粒細(xì)化程度不高，伸長率僅為260%；將退火溫度降低到240 ℃時(shí)，合金內(nèi)部僅發(fā)生了位錯(cuò)運(yùn)動(dòng)與重新組合，保留了較高的位錯(cuò)密度，晶粒得到細(xì)化，伸長率高達(dá)650%。

Fine-grained 2A97 alloy sheets were produced by thermo-mechanical processing. The effects of intermediate annealing temperature on the grain refinement and superplasticity were investigated by optical microscopy (OM), transmission electron microscopy (TEM) and high temperature tensile test. The results show that the fracture of sheet is observed when rolling at room temperature with a reduction of 22%. With increasing the rolling temperature, the degree of cracking gradually reduces. Non-fractured sheets can be obtained by enhancing the preheating temperature to 400 ℃, and then intermediate annealing the sheets for 1 h at 240, 300 and 400 ℃, respectively, when the rolling reduction reaches 88%. But the reheating temperatures have an obvious influence on the superplastic elongation. When the reheating temperature is 400 ℃, the obvious recrystallization occurs, which reduces the density of dislocations. Though non-fractured sheets with a total reduction of 92% are obtained, the superplastic elongation only reaches 260%, because of more deformation stored energy released and low grain refinement. High density of dislocations and a superplastic elongation of 650% are obtained when the reheating temperature decreases to 240 ℃, during which only the movement and reconfiguration of dislocations happen.

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