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Long term creep tests of diecast AZ91D and AM60B were conducted for periods of 30 days to nine months at temperatures up to 150°C. Stresses from 19 to 111 MPa were employed. Thermally activated creep did not occur when the temperature was below 100°C and the stress below 25 MPa. Under these conditions the creep rate eventually diminished to zero. AZ91D metal matrix composite specimens reinforced with 15 volume percent silicon carbide creep tested at 150°C exhibited much improved creep resistance over monolithic AZ91D.

The effects of low temperature thermal processing on diecast magnesium alloys AZ91D and AM60B were studied to determine the impact of manufacturing processes such as the baking of coatings on mechanical properties and corrosion resistance. For times less than 36 hours at temperatures up to 232°C little effect was observed on mechanical strength. Exposure to temperatures above 230°C was found to decrease salt spray corrosion resistance, particularly in alloy having higher residual element content. It was concluded that processing temperatures for diecast components in alloys AZ91D and AM60B be further limited to temperatures below 150° C whenever possible to insure maximum toughness and to offer a margin of safety.

In this study the solution annealed properties (T4) and solution annealed and aged properties (T6) of nominal 1/4-inch sections (6 mm) of die cast AZ91D and AM60B were studied, including the effects of aging time and temperature, and grainsize. An annealing time of 20 hours was found to be optimum for aging response and strength. Both the as-cast and heat treated properties of die cast specimens were superior to those of gravity-cast-and-heat-treated specimens. The T6 treatment did not improve the properties of die cast parts with nominal 6 mm sections due to grain growth induced by the T4 anneal. The effect of long time exposure to 250° F (120 °C) on the mechanical properties of as-cast die cast AZ91D and AM60B castings was also studied. It aged them to higher strengths than attainable by T6 treatments. Maximum strengthening occurred in 30-60 days; after 90 days overaging occurred.