Effects of Ni content on low cycle fatigue and mechanical properties of Al-12Si-0.9Cu-0.8Mg-xNi at 350°C

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2017-10, Vol.706, p.27-37
• Main Authors: Feng, Jian, Ye, Bing, Zuo, Lijie, Qi, Ruijuan, Wang, Qudong, Jiang, Haiyan, Huang, Rong, Ding, Wenjiang
• Format: Article
• Language: English
• Subjects: Al-Si alloys; Aluminum base alloys; Coarsening; Crack propagation; Elongation; Fatigue cracks; Fatigue failure; Fatigue strength; Fatigue tests; Heat resistant; High temperature; Low cycle fatigue; Mechanical properties; Microcracks; Microstructure; Permanent mold casting; Tensile strength; Thermal stability
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2017.08.114

In order to study the effects of ε-Al3Ni phase on elevated temperature properties, Al-12Si-0.9Cu-0.8Mg-xNi alloys with Ni contents of 1.0%, 2.5% and 4.0%, respectively, were prepared by gravity casting and their microstructure, tensile and low cycle fatigue properties at 350°C were investigated. The results show that the microstrucure mainly consists of α-Al, eutectic Si, ε-Al3Ni, δ-Al3CuNi, and Q-Al5Cu2Mg8Si6 phase. Thermodynamic calculation indicates that the ε-Al3Ni weight fraction increases with Ni contents while other phase contents are kept constant, and this result is consistent with the microstructure and XRD analysis. With the increase of ε-Al3Ni content, the tensile strength at 350°C increases from 94MPa to 116MPa, while the elongation decreases from 2.8% to 2.0%. The Al-Si alloy with 2.5% Ni exhibits the optimal low cycle fatigue property with a fatigue strength coefficient of 198.29MPa and fatigue strength exponent of − 0.1295. The coarsening of ε-Al3Ni phase is obvious with a higher Ni content of 4.0%, and the debonding of coarse ε-Al3Ni phase accelerates the propagation of micro-cracks and degrades the fatigue properties. The ε-Al3Ni phase is beneficial to the mechanical properties of the alloys and thermally stable during fatigue test at 350°C. •Only ε-Al3Ni phase is varied in the designed alloy.•The thermal stable ε-Al3Ni phase is beneficial to the tensile strength.•The volume fraction and size of the Al3Ni phase dominate the fatigue life.•The debonding of ε-Al3Ni phase is deleterious to the low cycle fatigue property.