Effect of beryllium and non-equilibrium heat treatment on mechanical properties of B319.0 alloy with 1.0%Fe

Abstract

B319.0 hypoeutectic alloy is a heat treatable Al -Si -Cu -Mg system with nominal composition Al -6Si -3 . 5Cu -0 . 3Mg and about 0 . 1 -1 . 2Fe. The purpose of this study was to determine the in uence of Be and non-equilibrium heat treatment on the microstructure and mechanical properties of B319.0 alloys with a higher Fe (1 . 0 wt-%) content. Results indicate that Be additions can reduce the amount and average length of iron bearing phases, can transform some platelet like shapes (b-Al 5 FeSi) of iron intermetallic phase to comparatively harmless Chinesescript shapes (a-Al 8 Fe 2 Si), and can also re ne the eutectic silicon. High temperature solution heat treatment(" 510°C) may not only completely dissolve the Al 2 Cu intermetallics, but may also cause dissolution and fragmentation behaviour in b-phase platelets and consequently reduce their volume fraction. Because the b-phase platelets are smaller in the Be-containing alloy under identical conditions, their dissolution behavior is more obvious than that in Be-free alloy. However, if deterioration of the mechanical properties is to be avoided, the solution temperature should be lower than the interdendritic melting temperature which resulted in an ultra ne eutectic phase on quenching. DSC and electrical conductivity analysis showed that the combined effect of Be additive and non-equilibrium heat treatment caused signi cant increase in the precipitation kinetics of B319.0 alloy. Fractographic analysis of tensile specimens revealed that fracture processes were mainly initiated by nucleation at b-Al 5 FeSi platelets as a result of their cracking and decohesion from the matrix. Therefore, adding Be to B319.0 alloy and optimising the solution heat treatment could result in fewer fracture initiating sites and greater precipitation of strengthening phases, with a consequent improvement in tensile properties.MST/5922

Microstructure and mechanical behavior of Al9Si0.8Fe alloy with different Mn contents

“…Cr, Co, Be, Mo and Mn) that cause grain refinement or modify the eutectic silicon phase are added in order to improve the strength/ductility of these alloys and reduce the harmful effect of iron phases [3,[13][14][15][16]. Additionally, beryllium changes the morphology of Fe-rich intermetallic compounds from needle or platelike to Chinese script or polygons, which is beneficial to the microstructure of the material because fracture initiating sites are mostly located on the coarse β-phase platelets [17,18].…”