The tensile properties and fatigue behavior of an Al-Zn-Mg-Cu alloy were investigated by performing tensile tests and fatigue crack propagation （FCP） tests. The tensile results show that lower aging temperature modi...The tensile properties and fatigue behavior of an Al-Zn-Mg-Cu alloy were investigated by performing tensile tests and fatigue crack propagation （FCP） tests. The tensile results show that lower aging temperature modified retrogression and re-aging （RRA） process enhances the elongation, but reduces the strength of the alloy, as compared to conventional RRA process which employs peak aging temperature. Both ductility and strength, however, are increased by employing a natural aging prior to re-aging based on the former modified RRA process. Fatigue test results show that both routes reduce FCP rate. Especially, the lower re-aging temperature modified RRA process obtains the lowest FCP rate. Natural aging treatment could enhance the nucleation rate of GP zones. A large amount of GP zones could be cut by dislocations, which is responsible for the highest tensile strength and elongation, as well as lower FCP rate.展开更多
在传统的回归再时效(retrogression and re-aging,RRA)工艺(峰时效)基础上降低预时效或再时效温度,对Fe和Si杂质含量高的超高强Al-Zn-Mg-Cu合金挤压棒材进行RRA处理,通过拉伸性能和疲劳性能测试以及扫描电镜和透射电镜观察,研究RRA工艺...在传统的回归再时效(retrogression and re-aging,RRA)工艺(峰时效)基础上降低预时效或再时效温度,对Fe和Si杂质含量高的超高强Al-Zn-Mg-Cu合金挤压棒材进行RRA处理,通过拉伸性能和疲劳性能测试以及扫描电镜和透射电镜观察,研究RRA工艺对合金力学性能与组织的影响。结果表明:降低预时效或再时效温度都可明显提高该合金的塑性和抗疲劳损伤性能,略微降低合金的抗拉强度。采用峰时效温度(120℃)RRA处理后的合金,晶内的主要析出相为尺寸较大的η′相,不能被位错切割,合金强度较高(674 MPa),但塑性和抗疲劳损伤性能差,伸长率为11.1%,最终应力强度因子幅值ΔK=26.8 MPa·m1/2;降低时效温度可增加析出相中GP区粒子的比例,减小η′相的尺寸,从而提高塑性变形能力以及抗疲劳损伤性能。展开更多
本文采用Lagrange乘数法获得了琴生不等式的加强形式:设a_i>0(i=1,…,n),如果r>1,那么(sum from a_i)~r≥sum from a_i^r-+(n^r-n)[1/n(sum from a^(-1)]^(-r)、如果o<r<1或r≤log_n(n-(n^2-4))~1/2》/2那么(sum from a_i)~...本文采用Lagrange乘数法获得了琴生不等式的加强形式:设a_i>0(i=1,…,n),如果r>1,那么(sum from a_i)~r≥sum from a_i^r-+(n^r-n)[1/n(sum from a^(-1)]^(-r)、如果o<r<1或r≤log_n(n-(n^2-4))~1/2》/2那么(sum from a_i)~r≤sum from a r/i+(n^r-n)[1/n(sum from a_i^(-1)]^(-r)。由此建立了正定矩阵的行列式的一些推广结果。展开更多
基金Project(51171209)supported by the National Natural Science Foundation of ChinaProject(2012CB619506)supported by the National Basic Research Program of Chinasupported by the 2011 Program of Nonferrous Metals and Materials,China
文摘The tensile properties and fatigue behavior of an Al-Zn-Mg-Cu alloy were investigated by performing tensile tests and fatigue crack propagation （FCP） tests. The tensile results show that lower aging temperature modified retrogression and re-aging （RRA） process enhances the elongation, but reduces the strength of the alloy, as compared to conventional RRA process which employs peak aging temperature. Both ductility and strength, however, are increased by employing a natural aging prior to re-aging based on the former modified RRA process. Fatigue test results show that both routes reduce FCP rate. Especially, the lower re-aging temperature modified RRA process obtains the lowest FCP rate. Natural aging treatment could enhance the nucleation rate of GP zones. A large amount of GP zones could be cut by dislocations, which is responsible for the highest tensile strength and elongation, as well as lower FCP rate.
文摘在传统的回归再时效(retrogression and re-aging,RRA)工艺(峰时效)基础上降低预时效或再时效温度,对Fe和Si杂质含量高的超高强Al-Zn-Mg-Cu合金挤压棒材进行RRA处理,通过拉伸性能和疲劳性能测试以及扫描电镜和透射电镜观察,研究RRA工艺对合金力学性能与组织的影响。结果表明:降低预时效或再时效温度都可明显提高该合金的塑性和抗疲劳损伤性能,略微降低合金的抗拉强度。采用峰时效温度(120℃)RRA处理后的合金,晶内的主要析出相为尺寸较大的η′相,不能被位错切割,合金强度较高(674 MPa),但塑性和抗疲劳损伤性能差,伸长率为11.1%,最终应力强度因子幅值ΔK=26.8 MPa·m1/2;降低时效温度可增加析出相中GP区粒子的比例,减小η′相的尺寸,从而提高塑性变形能力以及抗疲劳损伤性能。
文摘本文采用Lagrange乘数法获得了琴生不等式的加强形式:设a_i>0(i=1,…,n),如果r>1,那么(sum from a_i)~r≥sum from a_i^r-+(n^r-n)[1/n(sum from a^(-1)]^(-r)、如果o<r<1或r≤log_n(n-(n^2-4))~1/2》/2那么(sum from a_i)~r≤sum from a r/i+(n^r-n)[1/n(sum from a_i^(-1)]^(-r)。由此建立了正定矩阵的行列式的一些推广结果。
