Alloy Design for Semi Solid Metal Forming

Abstract

Semi-solid metal forming is more than 40 years old but its full potential to near net shape form high strength aluminium alloys has been realised only to a limited degree. Alloys developed for traditional manufacturing processes were initially used but it became apparent that alloys specific to SSM forming needed to be developed. The main alloy development criteria revolved around SSM processing temperature, solid fraction (fs) versus temperature sensitivity and age hardening potential. This methodology while sound does not fully address the unique processing behaviour of SSM forming. By its very nature SSM requires the controlled solidification of a part of the melt before forming. From basic solidification fundamentals this results in the enrichment of the remaining liquid with alloying elements. During the forming process segregation of liquid phase essentially produces a component with very different compositions in the regions where the liquid solidifies last. From recent work completed on a wide range of standard alloy systems it has become apparent that this segregation effect has a significant impact on aging behaviour and strength. Low melting point structures formed in the these regions result in localised melting in the grain boundary region and along areas of gross liquid segregation during solution heat treatment, contributing to the poor mechanical properties. Although this behaviour can be addressed using modified heat treatment, this cannot be applied to all current alloy systems. Alloy design for SSM forming must take these phenomena into account in order to develop and or specify aluminium alloys with acceptable mechanical properties.

The Solution Heat Treatment of Rheo-High Pressure Die Cast Al-Mg-Si-(Cu) 6xxx Series Alloys

“…The 6111 aluminium alloy needed longer times than the 6013 aluminium alloy in order to eliminate the peaks and this can be attributed to the 6013 lower excess Si and Cu contents as compared to those of the 6111 (Table 1). Even though the DSC results in Figures 4 and 5 showed that the eutectic melting peaks that cause incipient melting can be eliminated for both alloys, there might still possibly be incipient melting in the liquid segregated areas (SLS and CLS) even after the two step heat treatment [13]. This is due to the higher alloying elements content in these areas.…”

Progress of Semi-Solid Processing of Alloys and Composites in China

“…For instance, there are various requirements for automotive components, some need high strength and elongation, while some need high fatigue resistance, corrosion resistance and/or wear resistance. Even though some materials have been successfully developed, different material systems are highly desired to fulfill more requirements for industrial applications [78,79]. Also, the criterion for assessing the processability of materials for SSP is also needed to verify their applicability [80,81].…”

Current Progress in Rheoforming of Wrought Aluminum Alloys: A Review

“…The common approaches to develop new alloys mostly relied on CALPHAD and targeted experiments [133][134][135][136], which can not develop a large number of suitable alloys rapidly. The Material Genomic technology such as materials' design softwares and high-throughput methods to experimentally validate the candidate alloys are needed to exploit this capability effectively.…”