ffects of solution temperature on mechanical properties of 319.0 aluminum casting alloys containing trace beryllium

Abstract

The effects of beryllium (Be) and solution temperature on the morphologies of iron intermetallics, silicon particles, and copper intermetallics, relative to the mechanical properties of 319.0 alloys, were investigated. The experimental results indicated that adding Be to the alloy can raise the Al–Al₂Cu eutectic melting temperature, change some plateletlike shape (βndash;Al₅FeSi) of iron intermetallics to comparatively harmless Chinese-script morphologies (α–Al₈Fe₂Si), and reduce the amount and average length of βndash;Al₅FeSi platelets. During high-temperature solution treatment (>500 °C), the thinner and smaller the β–Al₅FeSi platelets were, the faster they dissolved and fragmented. However, where the solution temperature exceeded the Al–Al₂Cu eutectic melting point, the Al–Al₂Cu eutectic melted and resulted in an ultrafine eutectic phase on quenching, which deteriorated mechanical properties. The fracture behavior of 319 alloy was affected by the morphologies of the iron intermetallics, silicon particles, and copper intermetallics. Fractographic analysis of tested compact tension specimens revealed that the fracture processes were mainly initiated by void nucleation at β–Al₅FeSi platelets as a result of their cracking and decohesion from the matrix. Adding Be to the 319.0 alloy and optimizing the solution temperature could significantly decrease the number of fracture-initiation sites of β–Al₅FeSi platelets and improve the tensile properties and fracture toughness.