The effects of solution heat treatment on the microstructure and hardness of an aluminum-4% copper alloy with added nickel and tin

Abstract

This study delves into the investigation of intermetallic compounds, specifically Al3Ni, Al3Sn, Al2Cu, Ni3Al, and their formation during the alloying additions and heat treatment procedures of Al-4%Cu alloy with the addition of Ni and Sn. After manufacturing, an extensive range of tests, encompassing hardness assessments, SEM and XRD analysis, and optical microscopy, were executed. The introduction of Nickel (Ni) and Tin (Sn) into the base alloy resulted in a gradual and significant enhancement in hardness, with Alloy 3 exhibiting the most remarkable improvement, showcasing a 214.18 % increase in hardness attributed to higher concentrations of Ni and Sn. Then, heat treatment was carried out that encompassed an initial homogenization phase at 400 °C for a duration of 8 h, followed by precise water quenching. Subsequently, controlled aging precipitation was conducted at 150 °C with distinct time intervals. Comparative analyses of the effect of heat treatment on the hardness values revealed substantial improvements whereas base alloy showed a 67.55 % improvement after the heat treatment. On the other hand, Alloy 1, Alloy 2, and Alloy 3 indicated a 73.26 %, 36.03 %, and 31.22 % enhancement of hardness values respectively. The heat treatment process aimed to meticulously explore the intricate influences of Ni and Sn on the age-hardening process, with specific consideration to identifying the optimal aging time. The incorporation of Ni and Sn into the alloys led to the formation of intermetallic compounds, effectively impeding dislocation movement. Remarkably, Alloy 1 with lower Ni and Sn contents exhibited the most favorable response to the heat treatment, demonstrating a substantial 73.26 % increase in hardness at the optimal aging time. SEM images unveiled the formation of finer precipitates resulting from the aging treatment. This study offers valuable insights into the impact of alloying additions and heat treatment on the microstructure and hardness properties of Al-4%Cu alloys, with potential implications in the fabrication of advanced materials.