Characterization of Magnesium Automotive Components Produced by Super-Vacuum Die Casting Process

Abstract

Magnesium automotive components are currently produced by high pressure die casting. These castings cannot be heat-treated to improve the strength and ductility mainly due to the casting imperfections such as porosity and inclusions created by the air entrainment during the turbulent mold filing. These imperfections also prevent magnesium components to be used for highly stressed body components. Efforts were made to produce high integrity magnesium castings through a Super-Vacuum Die Casting process. The AZ91D castings were found to have very low porosity and can be heat-treated without blisters. The tensile properties of the castings were satisfactory. The mechanical properties and thermal analysis indicate that the conventional heat treatment procedure needs to be optimized for such thin sectioned and rapidly solidified castings which have very fine microstructures.

Heat treatment of vacuum high pressure die cast magnesium alloy AZ91

“…The tensile properties measured in this work are consistent with those reported for supervacuum die cast AZ91 by Sadayappan et al, 11 in which decreases in both the yield strength and the tensile strength after heat treatment were also observed. Sadayappan et al 11 attributed the decrease in yield strength after heat treatment to grain growth.…”

“…In both studies, significant age hardening was observed and was related to the precipitation of Mg 17 Al 12 , but no tensile properties were reported. Sadayappan et al 11 applied heat treatment to AZ91 produced by supervacuum die casting, but an improvement in strength was not observed. They attributed the decrease in yield strength after heat treatment to grain growth, in agreement with the assessment of Wang et al 17 of the heat treatment on rheo die cast samples.…”

“…It should be noted that vacuum casting of itself can significantly improve the properties of castings by reducing the porosity. 11,12 Another approach is the adoption of new heat treatment procedures, e.g. reducing the temperature and time of solution treatment.…”

An ICME Method for Predicting Phase Dissolution During Solution Treatment in Advanced Super Vacuum Die Cast Magnesium Alloys

“…Thus, precipitation hardening has not previously been a viable strengthening mechanism for HPDC Mg components. However, with the advent of super vacuum die casting (SVDC) blister-free heat treatable HPDC components are now possible [14][15][16], providing new approaches to alloying and heat treatment to improve the strength of high production volume SVDC Mg components [16][17][18]. This necessitates the study of solution treatment processes for SVDC Mg castings.…”

FY2017 Materials Annual Progress Report

“…Research on heat treatment of die-cast Mg alloys has been limited due to the blistering that occurs when entrapped air expands during solution treatment. A new processing technology, SVDC for Al and Mg alloy components (Sadayappan et al 2009, Luo et al 2010, significantly reduces or eliminates air entrapment thus enabling heat treatment of die-casting alloys and components. This advanced processing route offers new approaches for alloy development and improved Mg component properties.…”