多元Al-7.5Si-4Cu合金热疲劳裂纹萌生与扩展行为的研究

刘光磊; 司乃潮; 孙少纯; 张志坚; 吴勤方

doi:10.3724/SP.J.1037.2012.00484

金属学报 >

2013 , Vol. 49 >Issue 3: 303 - 310

DOI: https://doi.org/10.3724/SP.J.1037.2012.00484

论文

多元Al-7.5Si-4Cu合金热疲劳裂纹萌生与扩展行为的研究

刘光磊 ,
司乃潮 ,
孙少纯 ,
张志坚 ,
吴勤方

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1)江苏大学材料科学与工程学院镇江 212013
2)苏州明志科技有限公司, 苏州 215217

刘光磊, 男, 1983年生, 博士生

收稿日期: 2012-08-13

修回日期: 2012-12-24

网络出版日期: 2013-03-11

基金资助

科技部科技型中小企业技术创新基金项目09C26279200863和江苏省科技成果转化专项资金项目BA2011084资助

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THERMAL FATIGUE CRACK INITIATION ANDPROPAGATION OF MULTIELEMENTAl-7.5Si-4Cu ALLOY

LIU Guanglei ,
SI Naichao ,
SUN Shaochun ,
ZHANG Zhijian ,
WU Qinfang

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1) School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013
2) Suzhou Mingzhi Technology Ltd., Suzhou 215217

Received date: 2012-08-13

Revised date: 2012-12-24

Online published: 2013-03-11

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摘要

研究了不同热处理状态的多元Al-7.5Si-4Cu合金在室温至350 ℃下的热疲劳行为, 利用OM和SEM对合金的热疲劳裂纹形貌进行了观察.结果表明: T6处理后多元Al-7.5Si-4Cu合金的热疲劳性能优于铸淬+时效态和铸态. 热疲劳裂纹均萌生于V型缺口处, 热应力诱导使组织氧化疏松最终成为裂纹萌生源. 裂纹扩展前期为沿晶生长, 主要靠裂尖钝化-尖锐化引起裂纹扩展; 裂纹扩展后期为沿晶、穿晶混合生长, 以裂尖钝化-尖锐化和裂尖前沿空洞连体复合方式扩展. 扩展行径受Si相的形状和位向影响, 与Si相短轴方向夹角大于60°为“绕墙”扩展; 与长轴方向夹角大于60°为“穿墙”扩展. 氧化作用在裂纹萌生期表现显著, T6态合金抗氧化性能最优.

关键词： 多元Al-7.5Si-4Cu; 热疲劳; 萌生; 扩展行径; 氧化

本文引用格式

刘光磊 , 司乃潮 , 孙少纯 , 张志坚 , 吴勤方 . 多元Al-7.5Si-4Cu合金热疲劳裂纹萌生与扩展行为的研究[J]. 金属学报, 2013 , 49(3) : 303 -310 . DOI: 10.3724/SP.J.1037.2012.00484

Abstract

With the rapid development of automotive industry, the requirements for engine performance hasbecome increasingly higher and higher, such as dynamic performance, environmental performance, fuel economyperformance and so on. Obviously, using lighter aluminum engine has become the future of the automobile industry.When start or stop the engine, the engine generates drastic temperature field that will make parts of the enginecomponents into the plastic deformation zone. If the engine components continue like this, extremely high thermalstrain will cause the thermal fatigue failure of aluminum alloy for automotive engine. Thermal fatigue is a more seriousform of material fatigue failure. The thermal fatigue is prevalent in many important engine castings, such as cylinderbody, cylinder head, piston and so on. Therefore, study on thermal fatigue properties of multivariate Al-Si-Cu castalloy has the most important significance. Based on this thermal fatigue behaviors of multivariate Al-7.5Si-4Cu alloys under different heat treatmentwere investigated in the temperature ranges of room temperature to 350℃. Thethermal fatigue cracks of the tested specimens were observed using OM and SEM. The results demonstrate that thermalfatigue properties of the alloy after T6 heat treatment is better than the alloy after cast-quenching+aging heattreatment and the cast alloy. Reasonable heat treatment process can improve the strength, the plasticity and thethermal fatigue property of multivariate Al-7.5Si-4Cu alloy, including reduce the rate of crack propagation.The main reason of crack initiation is oxidative microstructure induced by thermal stress. Fatigue crack expands alongthe grain boundary bypassivation-sharpen of crack tip in the early. In the late, fatigue crack expands with both intergranular way andtransgranular way by passivation-sharpen of crack tip and siamesed holes on front edge of crack tip. The Si phasescan affect fatigue crack propagation. When the angle between the fatigue crack propagation and the short axis of theSi phase is more than 60°, fatigue crack expandsas “bypass-wall expansion”. When the angle between the fatiguecrack propagation and the long axis of the Si phase is more than 60°, fatigue crack expands as “through-wallexpansion”. Oxidation behavior effects significantly at the crack initiation period. After T6 heat treatment, theantioxidant property of multivariate Al-7.5Si-4Cu alloy is the best. Oxidation kinetics curves of multivariateAl-7.5Si-4Cu alloy under the different heat treatment are all logarithmic relationship.

Key words： multivariate Al-7.5Si-4Cu; thermal fatigue; initiation; propagation path; oxidation

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