Controlled Diffusion Solidification of 2024, 6082 and 7075 Al Alloys via Tilt-Pour Casting Process

Abstract

Controlled diffusion solidification (CDS) is an innovative casting route for Al alloys to obtain a cast part with a non-dendritic morphology of the primary Al phase during solidification, similar to those obtained in the semi-solid rheocasting process. The process involves mixing two alloy melts with specific individual compositions and temperatures to produce the desired final alloy by mixing and immediately casting in a mould. CDS enables sound shaped casting of Al based wrought and cast alloys with a non-dendritic microstructure. The two pre-cursor alloys will have to be chosen from a critical study of the various isopleths of the multi-component phase diagrams for the respective alloys along with laboratory experiments. Further, the favorable melt superheat temperatures of the two pre-cursor alloys were evaluated from laboratory experiments as well. A tilt-pour mould designed and validated to cast tensile test bars was used for the study. The aim of the study was to demonstrate the feasibility of manufacturing sound shaped castings via the CDS route for alloys which have been impossible to shape cast in a permanent mould process due to the detrimental hot-tearing problem during solidification. The present work defines process conditions to enable shaped casting of the Al wrought alloys 2024, 6082 and 7075 by the tilt-pour casting technique. Sound casting and a favorably non-dendritic microstructure were obtained for these alloys during solidification in a ceramic crucible as well as in a metallic mould via the tilt-pour casting process. Further work is underway to optimize various process conditions and develop new heat treatment cycles for parts cast by CDS to maximize mechanical properties for these alloys.