(中南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410083)
摘 要: 通過(guò)拉伸試驗(yàn)及平面應(yīng)變斷裂韌性測(cè)試，研究不同時(shí)效制度對(duì)2A97合金強(qiáng)韌性的影響，并利用透射電鏡和掃描電鏡對(duì)合金的微觀組織及斷口形貌進(jìn)行觀察。結(jié)果表明：2A97合金在135 ℃單級(jí)時(shí)效時(shí)斷裂韌性較好，但強(qiáng)度偏低；雙級(jí)時(shí)效可促進(jìn)強(qiáng)度的提高,但第二級(jí)時(shí)效溫度過(guò)高時(shí)(175 ℃)，斷裂韌性迅速下降，經(jīng)過(guò)(135 ℃, 36 h)+(150 ℃, 18 h)時(shí)效，可得到較好的強(qiáng)韌性匹配，其σb、σ0.2和KIC 分別為547 MPa、489 MPa和28.9 MPa·m1/2。2A97合金中的主要強(qiáng)化相為δ ′相和T1相。δ ′相易共面滑移而引起應(yīng)力集中，對(duì)合金韌性不利；T1相能有效地阻止位錯(cuò)滑移,對(duì)合金強(qiáng)度有顯著提高。2A97合金在時(shí)效初期以穿晶和沿晶混合型斷裂為主，斷口表現(xiàn)出明顯的分層特征，具有較好的韌性；隨時(shí)效時(shí)間的延長(zhǎng)，析出相的體積分?jǐn)?shù)、尺寸以及臨界分切應(yīng)力增大，所造成的應(yīng)力集中更明顯，同時(shí)晶界平衡相增多，晶界無(wú)沉淀帶加寬，沿晶斷裂比例增多，合金韌性急劇下降。
關(guān)鍵字:
fracture toughness of 2A97 aluminum-lithium alloy
（School of Materials Science and Engineering, Central South University, Changsha 410083, China）
Abstract:The effect of ageing treatment on the strength and fracture toughness of 2A97 alloy was investigated by tensile test and plane-strain fracture toughness experiments. The microstructures and fracture morphologies were observed and analyzed by TEM and SEM. The results indicate that the 2A97 alloy obtains a preferable fracture toughness of in single aging at 135 ℃，but its strength is relatively low. The duplex aging enhances the strength, while the fracture toughness deteriorates at an excessive temperature as 175 ℃. The 2A97 alloy can obtain the superior combination of the strength and toughness after (135 ℃, 36 h)+(150 ℃, 18 h) aging treatment, with the σb, σ0.2and KIC of 547 MPa, 489 MPa and 28.9 MPa·m1/2, respectively. The δ′ and T1 phases are the major precipitates in the 2A97 alloy. The δ′ phase may induce the stress localization and thus deteriorate the toughness, while the T1 phase can resist the slip of dislocation effectively and significantly enhance the strength. At the early stage, it primarily presents a hybrid of transgranular and intergranular fractures with obvious delamination crackings at the fracture surfaces, which indicates a high level of toughness. The volume fraction, size and critical resolved shear stress of precipitations increase with prolonging the aging time, and lead to more severe stress localizations. In additions, the more equilibrium phases at grain boundaries, the wider PFZs together with the greater proportional of intergranular fractures result in a sharply reduce of fracture toughness.
Key words:
