(1. 中南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410083；
2. 中南大學(xué) 有色金屬材料科學(xué)與工程教育部重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410083)
摘 要: 采用疲勞強(qiáng)度及裂紋擴(kuò)展測(cè)試、掃描電鏡和電子背散射衍射等方法研究難溶結(jié)晶相分布特征對(duì)7020鋁合金型材疲勞行為的影響。結(jié)果表明：合金中直徑小于2 μm的難溶結(jié)晶相占比較大，且數(shù)量較多；當(dāng)直徑大于4 μm的難溶結(jié)晶相較少時(shí)，疲勞強(qiáng)度可達(dá)113.3 MPa，比含較多大尺寸難溶結(jié)晶相的合金疲勞強(qiáng)度高16.4%。當(dāng)應(yīng)力強(qiáng)度因子ΔK=10 MPa·m1/2時(shí)，含較多大尺寸難溶結(jié)晶相比含密集且細(xì)小的合金裂紋擴(kuò)展速率快21.0%。直徑在3~17 μm的粗大難溶結(jié)晶相在疲勞循環(huán)中因自身開裂或與基體界面脫粘而易形成裂紋源，其中直徑在3~7 μm之間的難溶結(jié)晶相加速疲勞裂紋擴(kuò)展的頻率最高。尺寸細(xì)小的難溶結(jié)晶相能均勻分散應(yīng)力，增加裂紋斷面粗糙度，提高合金疲勞性能。難溶結(jié)晶相也能影響合金再結(jié)晶程度和晶界特征，再結(jié)晶分?jǐn)?shù)和大角度晶界降低時(shí)可以提高疲勞裂紋擴(kuò)展抗力。
關(guān)鍵字: 7020鋁合金；難溶結(jié)晶相；疲勞強(qiáng)度；疲勞裂紋擴(kuò)展
（1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China）
Abstract:The influence of intermetallic particles on fatigue behavior of 7020 aluminum alloy profile was investigated by fatigue strength test, fatigue crack growth test, scanning electron microscopy and electron back scattering diffraction technique. The results show that the fatigue strength of the alloy containing amounts of intermetallic particles with a diameter of less than 2 μm and few particles with a size of greater than 4 μm reaches 113.3 MPa, which is 16.4% higher than that of the alloy with more large-sized intermetallic particles. The fatigue crack growth rate of the alloy containing more large-size intermetallic particles is 21.0% faster than that of the alloy with dense and fine intermetallic particles. The coarse intermetallic particles with a diameter of 3 to 17 μm are likely to form fatigue crack initiation due to self-cracking or debonding from the substrate during fatigue cycles. And the particles with a diameter between 3 and 7 μm have the highest frequency of accelerating fatigue crack growth. The intermetallic particles with small size can evenly distribute stress, increase the roughness of the crack section, and improve the fatigue performance of the alloy. The intermetallic particles also affect the recrystallization fraction and grain boundary characteristics of the alloy. When the recrystallization fraction and high angle grain boundary of the alloy are reduced, fatigue crack propagation resistance can be improved.
Key words: 7020 aluminum alloy; intermetallic particle; fatigue strength; fatigue crack growth
