Thermomechanical behavior of Al-Cu-Si commercial alloy modified with rare earths

Abstract

The effect of cerium/lanthanum rare earths on the microstructural and mechanical behavior of an automotive grade AA319 aluminum alloy was studied at room and hot working conditions. The microstructural results in the modified AA316 aluminum alloys showed that Ce/La additions formed stable micrometric phases at room and hot working conditions, whilst a reductionin the total area of the eutectic-Si phase of up to 75\% was observed in comparison with the reference alloy. The effect of the Ce/La addition in the aluminum alloys produced an increment in hardness and UTS under room temperature; however, their mechanical behavior was improved in hot working conditions. This improvement is attained to the presence of well dispersed Ce/La phases increasing the amount of the $\theta$'-phase (Al$_2$Cu) across the aluminum matrix. The $\theta$'-phase (Al$_2$Cu) interferes directly with crack diffusion of the solid in two crystallographic directions. Additionally, it was observed through transmission electron microscopy, that Ce/La presence alters the kinetics of precipitation in the formation of the coherent $\theta$-phase from the $\theta$'-phase.