(中南大學(xué) 材料科學(xué)與工程學(xué)院，長沙 410083)
摘 要: 采用掃描電鏡(SEM)、差熱分析儀(DSC)和X射線衍射儀(XRD)，分析快速凝固過共晶Al-Si合金粉末顯微組織和結(jié)構(gòu)特征及其在不同退火溫度和保溫時間條件下過飽和固溶Si元素析出和Si相粗化行為。結(jié)果表明：快速凝固Al-Si合金顯微組織中細(xì)小的塊狀初晶Si相和針狀共晶Si相均勻分布在α(Al)基體中；氣霧化過程獲得的高過冷度導(dǎo)致Al基體晶格發(fā)生畸變，其在退火過程中得到一定程度的緩解。對快速凝固Al-Si合金中析出Si相粗化行為的分析發(fā)現(xiàn)，析出Si相隨退火溫度升高或保溫時間延長而不斷粗化；但其粗化不符合經(jīng)典LSW理論(粗化指數(shù)n為3)，粗化機制接近由擴散速率較快的界面擴散控制(n接近2)。此外，退火溫度僅對粗化速率常數(shù)和激活能有較大影響，而對粗化指數(shù)的作用不明顯。
關(guān)鍵字: 鋁硅合金；顯微組織；快速凝固；粗化；顯微硬度
（School of Materials Science and Engineering, Central South University, Changsha 410083, China）
Abstract:The microstructure characteristics of rapidly solidified hypereutectic Al-Si alloy were analyzed as function of annealing temperature and holding time by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The precipitation and coarsening of supersaturated Si element were also investigated. The results indicate that the microstructure of rapidly solidified Al-Si alloy is composed of fine block-like primary and needle-like eutectic Si phase dispersed homogeneously in the α(Al) matrix. The structural distortion of the α(Al) matrix is observed owing to large solidification rate as a result of gas atomization. While, the structural distortion is released after annealing. The studies of coarsening of supersaturated Si in the matrix suggest that the precipitated Si phase coarsens with increasing annealing temperature or prolonging holding time. However, the coarsening behavior is different to the classical LSW theory. The coarsening mechanism is more likely to be controlled by interface diffusion with coarsening exponent near 2. Additionally, the annealing temperature only affects the coarsening rate constant and activation energy, but less affects the coarsening exponent.
Key words: aluminum-silicon alloy; microstructure; rapid solidification; coarsening; microhardness
