超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理
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摘要
通过超声疲劳试验探究超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响。同时,从应力集中、残余应力、晶粒细化等3个因素来探究超声冲击改善MB8镁合金焊接接头超高周疲劳性能的机理。结果表明:在1.0×108疲劳寿命下,焊态试样疲劳强度为31.62 MPa,冲击态试样疲劳强度为39.81 MPa,冲击态试样疲劳强度相较于焊态提高了26%。这说明超声冲击可以明显提高MB8镁合金焊接接头超高周疲劳性能。焊态试样焊趾处应力集中系数K_(t1)=1.95,冲击态试样焊趾处应力集中系数K_(t2)=1.67,应力集中系数降低了14.4%,所以超声冲击可以降低焊趾处的应力集中程度。超声冲击后试样焊趾处的应力由残余拉应力转变成残余压应力。超声冲击细化了焊趾表面晶粒从而改善了MB8镁合金焊接接头的超高周疲劳性能。
The effect of ultrasonic impact treatment(UIT) on ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint was investigated by ultrasonic fatigue test. At the same time, the mechanism of UIT improving the ultra-high cycle fatigue properties of MB8 magnesium alloy welded joints was investigated from three factors, inc luding stress concentration, residual stress and grain refinement.The results show that under the fatigue life of 1× 108 cycles, the fatigue strength of the ultrasonic impact treated specimen is 39.81 MPa,which is 26% higher than 31.62 MPa of the as-welded. This indicates that UIT can obviously improve the ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint. The weld toe stress concentration factor of as-welded specimen(K_(t1)) is 1.95 and that of ultrasonic impact treated specimen(K_(t2)) is 1.67, which is reduced by 14.4%. The UIT can reduce the stress concentration of the weld toe.After UIT, the stress at the toe of the specimen changes from residual tensile stress to residual compressive stress. UIT ref ines surface grain of the weld toe to improve ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint.
The effect of ultrasonic impact treatment(UIT) on ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint was investigated by ultrasonic fatigue test. At the same time, the mechanism of UIT improving the ultra-high cycle fatigue properties of MB8 magnesium alloy welded joints was investigated from three factors, inc luding stress concentration, residual stress and grain refinement.The results show that under the fatigue life of 1× 108 cycles, the fatigue strength of the ultrasonic impact treated specimen is 39.81 MPa,which is 26% higher than 31.62 MPa of the as-welded. This indicates that UIT can obviously improve the ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint. The weld toe stress concentration factor of as-welded specimen(K_(t1)) is 1.95 and that of ultrasonic impact treated specimen(K_(t2)) is 1.67, which is reduced by 14.4%. The UIT can reduce the stress concentration of the weld toe.After UIT, the stress at the toe of the specimen changes from residual tensile stress to residual compressive stress. UIT ref ines surface grain of the weld toe to improve ultra-high cycle fatigue properties of MB8 magnesium alloy welded joint.
引文
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[3]Zhang Hongxia(张红霞),Wang Wenxian(王文先),Su Juan(苏娟)et al.Rare Metal Materials and Engineering(稀有金属材料与工程)[J],2009,38(S3):187
[4]He Bolin(何柏林),Zhang Zhisen(张枝森),Xie Xuetao(谢学涛)et al.Journal of East China Jiaotong University(华东交通大学学报)[J],2016,33(5):51
[5]Yang F,Yin S M,Li S X et al.Materials Science and Engineering A[J],2008,491:131
[6]Kazuaki Shiozawaa,Tomoki Kashiwagi,Tutomu Muraic et al.Procedia Engineering[J],2010(2):183
[7]Yanga F,Lva F,Yanga X M et al.Materials Science and Engineering A[J],2011,528(6):2231
[8]Xu Daokui(许道奎),Liu Lu(刘路),Xu Yongbo(徐永波)et al.Acta Metallurgica Sinica(金属学报)[J],2007,43(2):144
[9]Yin Shuming(尹树明),Wang Chunhui(王春晖),Zhao Shuzhe(赵述哲)et al.Light Metals(轻金属)[J],2013(7):54
[10]Song Jiatong(宋佳曈).A Study of Very High Cycles Fatigue Properties of Wrought Magnesium Alloy and Its Welded Joint(变形镁合金及其焊接接头的超高周疲劳性能研究)[D].Dalian:Dalian Jiaotong University,2013
[11]Li Dong(李东),Chen Huaining(陈怀宁),Liu Gang(刘刚)et al.Transactions of the China Welding Institution(焊接学报)[J],2002,23(2):18
[12]Wang Dongpo(王东坡),Gong Baoming(龚宝明),Wu Shipin(吴世品)et al.Journal of East China Jiaotong University(华东交通大学学报)[J],2016,33(6):1
[13]Liu Suo(刘锁).Fatigue Properties and Shot Peening Process of Metal Materials(金属材料的疲劳性能与喷丸强化工艺)[M].Beijing:National Defense Industry Press,1977