(1. 江蘇大學(xué) 材料科學(xué)與工程學(xué)院，鎮(zhèn)江 212013；
2. 上海交通大學(xué) 金屬基復(fù)合材料國家重點(diǎn)實(shí)驗(yàn)室，上海 200240)
摘 要: 采用熔體直接反應(yīng)法，以工業(yè)7055鋁合金為基體，利用K2TiF6和K2ZrF6多組元制備Al3(Ti0.5Zr0.5)原位顆粒強(qiáng)化鋁基復(fù)合材料，再將復(fù)合材料經(jīng)過擠壓、固溶時(shí)效處理后進(jìn)行深冷時(shí)效循環(huán)處理。采用正交實(shí)驗(yàn)設(shè)計(jì)法研究降溫速度、處理時(shí)間和循環(huán)次數(shù)對復(fù)合材料顯微組織和力學(xué)性能的影響。采用差示熱分析儀對復(fù)合材料進(jìn)行低溫?zé)岱治觯捎肧EM和TEM對材料顯微組織進(jìn)行觀察。結(jié)果表明：材料從液氮溫度77 K升溫至165 K左右時(shí)出現(xiàn)了明顯的放熱峰，此溫度處出現(xiàn)了相變。熱計(jì)算結(jié)果表明該溫度下大量析出了S相(Al2CuMg)。深冷處理后復(fù)合材料內(nèi)部細(xì)小析出相數(shù)量增多，主要組分是η(MgZn2)相和η′(MgZn2′)相；隨著降溫速度、處理時(shí)間和循環(huán)次數(shù)增加，性質(zhì)不穩(wěn)定且硬度高的η′相數(shù)量減少，性質(zhì)穩(wěn)定硬度較低的η相數(shù)量增加。與未冷處理試樣相比，深冷時(shí)效循環(huán)處理后試樣的平均抗拉強(qiáng)度提高14.7%，沖擊韌性提高10.9%，伸長率提高50%，斷裂機(jī)制為韌窩型斷裂機(jī)制。當(dāng)試樣具有高強(qiáng)度、高韌性時(shí)，對應(yīng)的最優(yōu)冷處理參數(shù)為：降溫速度v為1 ℃/min、保溫時(shí)間t為24 h、循環(huán)次數(shù)N為1或2。當(dāng)試樣的伸長率最高時(shí)，對應(yīng)的參數(shù)為：v為10 ℃/min、t為36 h、N為1。復(fù)合材料強(qiáng)化機(jī)制為析出相強(qiáng)化、位錯(cuò)強(qiáng)化和細(xì)晶強(qiáng)化等。
關(guān)鍵字: 鋁基原位復(fù)合材料；深冷時(shí)效循環(huán)處理；顯微組織；力學(xué)性能
（1. School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China;
2. The State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China）
Abstract:The in-situ Al3(Ti0.5Zr0.5) composite was synthesized using K2TiF6 and K2ZrF6 components in 7055 aluminum alloy by melt direct reaction method. Cryogenic aging circular treatment (CACT) was performed after extrusion deformation and solution-aging heat treatment. The effects of cooling rate (v), processing time (t) and circular index (N) on the microstructure and mechanical properties of composites were studied by orthogonal experimental method. The composite was studied by differential scanning calorimetry (DSC) under cryogenic condition, and the microstructure of composite was studied by SEM and TEM. The result shows that when the specimen is heated from the cryogenic temperature (77 K) to about 165 K, there will be an obvious exothermic peak. The phase transforms from matrix to S phase (Al2CuMg). There are amounts of fine precipitates in the composites, the main components are regarded as η (MgZn2) and η′(MgZn2′) phases. With increasing the v, t and N, the amount of η′ phase that is unstable but hard will decrease, while the stable but soft η phase will increase. Compared with the sample without CACT, the average tensile strength (σb), impact toughness (ak) and elongation (δ) of the sample with CACT have been enhanced by 14.7%,10.9% and 50%, respectively. The main fracture mechanism is dimple one. When the samples with high σb and ak are acquired, the optimal CACT parameters are: v=1 ℃/min; t=24 h and N=1 or 2. When the samples with superior elongation are acquired, the corresponding CACT parameters are: v=10 ℃/min, t=36 h and N=1. The strengthening mechanisms of CACT composite are precipitation strengthening, dislocation strengthening and fine crystalline strengthening.
Key words: in-situ aluminum matrix composite; cryogenic aging circular treatment; microstructure; mechanical property
