多元Al-7Si-0.3Mg合金热疲劳裂纹萌生与扩展行为

Thermal Fatigue Crack Initiation and Propagation Behavior of Multicomponent Al-7Si-0.3Mg Alloys

摘要:

研究了在不同温度下的3种不同处理状态的多元Al-7Si-0.3Mg铝合金热疲劳性能，提出了用积分方法及割线法计算热疲劳裂纹扩展寿命，并对合金的热疲劳裂纹生长行为进行了分析。结果表明：温度变化对多元Al-7Si-0.3Mg铝合金的热疲劳裂纹扩展速率有直接的影响，添加了Cu、Mn、Ti等元素的多元Al-7Si-0.3Mg合金在细化变质处理和直接细化变质处理后的热疲劳性能优于铸态Al-7Si-0.3Mg合金。热疲劳裂纹的萌生需经历一定的孕育期，裂纹萌生于V型缺口处，当交变热应力超过合金的屈服强度σ_s时，沿着V型缺口的应力集中部位或缺陷处会出现不同类型的热疲劳裂纹，但有且只有1条主裂纹。当裂纹尖端扩展路径与第二相颗粒长轴方向形成小于45°的夹角时，裂纹扩展将沿着第二相颗粒的边缘继续向前扩展；当裂纹尖端扩展路径与第二相颗粒短轴方向形成小于45°的夹角时，裂纹将穿过第二相颗粒，继续向前扩展。

Abstract:

The thermal fatigue properties of multicomponent Al-7Si-0.3Mg aluminum alloys in three different treatment states at different temperatures were studied. The integral method and secant method were proposed to calculate the thermal fatigue crack propagation life, and the thermal fatigue crack growth behavior of the alloys was analyzed. The results indicate that the temperature change has a direct effect on the thermal fatigue crack propagation rate of the multicomponent Al-7Si-0.3Mg aluminum alloys. The thermal fatigue properties of the multicomponent Al-7Si-0.3Mg alloys with addition of Cu, Mn, Ti, and other elements after refinement and direct refinement are superior to those of the as-cast Al-7Si-0.3Mg alloys. The growth behavior of thermal fatigue cracks mainly includes the initiation and propagation of thermal cracks. The initiation of thermal fatigue crack requires a certain incubation period and the crack is generated at the V-notch. When the alternating thermal stress exceeds the yield strength σ_s of alloys, different types of thermal fatigue cracks appear at the stress concentration parts or at defects of the V-notch but with only one main crack. When the angle between the crack tip propagation path and the major axis direction of the second phase particle is less than 45°, the crack propagation extends further along the edge of the second phase particles; when the angle between the crack tip propagation path and the minor axis direction of the second phase particle is less than 45°, the crack passes through the second phase particle and extends forward.