(南昌航空大學(xué) 輕合金加工科學(xué)與技術(shù)國防重點(diǎn)學(xué)科實(shí)驗(yàn)室，南昌 330063)
摘 要: 采用銅模噴鑄與高溫退火相結(jié)合，研究快冷AZ91+SiC合金組織細(xì)化與高溫晶粒長大，揭示SiC顆粒對亞快速凝固鎂合金異質(zhì)形核及熱穩(wěn)定性的影響。結(jié)果表明：SiC可促進(jìn)亞快速凝固過程中異質(zhì)形核，阻礙凝固界面遷移，顯著細(xì)化噴鑄合金組織。400 ℃等溫退火后，組織從枝晶向等軸晶轉(zhuǎn)變并發(fā)生明顯晶粒長大，快冷AZ91合金保溫8 h后平均晶粒尺寸達(dá)78 μm。添加2%SiC后，晶粒長大得到有效控制，8 h退火處理后平均晶粒尺寸僅為22 μm。SiC的存在提高了基體中晶格畸變，退火組織中析出層片狀與粒狀共存的沉淀相。晶粒細(xì)化及SiC的添加提高了快冷鎂合金顯微硬度。隨退火時(shí)間延長，合金硬度下降。沉淀相的析出導(dǎo)致AZ91+2%SiC合金硬度增加，最高可達(dá)111HV，比AZ91合金的硬度提高63.2%。
關(guān)鍵字: 鎂合金；凝固；冷卻速率；異質(zhì)形核；晶粒長大
（National Defense Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:Using copper-mould spray casting and annealing techniques, microstructure refinement and grain growth at high temperature for quenched AZ91+SiC alloy were analyzed. Effects of SiC on heterogeneous nucleation of sub-rapid solidified alloy and thermal stability were elucidated. Results show that SiC promotes heterogeneous nucleation and inhibits interface migration. Grain size in spray casted alloy reveals significant reduction. After annealing at 400 ℃, dendrite transits to equiaxed grain, accompanied by obvious grain growth. The grain size of quenched AZ91 alloy after annealing for 8 h is 78 μm, whereas it reduces to 22 μm after adding 2%SiC, indicating the suppression of grain growth. The increase of lattice distortion by SiC generates lamellar and granular precipitations. Grain refinement and SiC increase the micro-hardness of quenched alloy and reduction occurs for longer annealing time. The maximum hardness of 111HV can be obtained in AZ91+2%SiC alloy due to precipitates, which increases by 63.2% than that of AZ91 alloy.
Key words: magnesium alloy; solidification; cooling rate; heterogeneous nucleation; grain growth
