Enhancing the precipitation hardening ability of Al-Mg-Ga-In-Sn alloy through low-temperature aging treatment

An experimental as-cast Al-Mg-Ga-In-Sn alloy, with unique combinations of high-strength, dissolvability, and manufacturability, has been developed as a structural oilfield material for hydraulic fracturing. The present study reports an exceptional aging hardening ability in which the Al-Mg-Ga-In-Sn alloy reached ~180 HV through aging between 80°C and 120°C. This significant hardening response has been attributed to dynamic changes in the precipitation. TEM observation and diffraction pattern analysis revealed that the as-cast specimen with a hardness of 142 HV exhibited numerous ~ 7 nm fine precipitates, which were identified as MgGa₂ and Mg₂Ga₅. Low-temperature aging, which led to a higher hardness of ~180 HV, resulted in the formation of L1₂-type coherent precipitates with an average size of about 3 nm. In contrast, only incoherent precipitates MgGa₂ and Mg₂Ga₅ with relatively large sizes of 6.5 nm to 14.2 nm were observed after aging between 170°C and 300°C, resulting in a major reduction in hardness. The present study also explored the precipitate evolution, progressing from L1₂-type coherent precipitates to stable incoherent precipitates of MgGa₂ and Mg₂Ga₅ during over-aging treatment at a low temperature. As these experimental as-cast specimen exhibited limited tensile properties due to brittle grain boundary phases, potential improvements are discussed for a greater use of such alloys beyond its historical use, largely through controlled reduction in alloying and improved processing over solely an as-cast condition.