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Understanding the creep and bolt load retention (BLR) behavior of promising Mg-Al alloys are crucial to developing elevated temperature resistance alloys. This is especially true for elevated temperature automotive applications with a prevalence of bolted joints. In this study, creep and fastener clamp load response of Mg-Al alloy AS41 was investigated and compared to that of Mg4Al and AS41 micro-alloyed with 0.15 % Ca. A compliance-creep approach was used to model the response of these Mg-Al alloys at bolted joints. The equation prediction of the BLR response and experimental results are in good agreement. AS41+0.15 Ca shows improved creep and BLR properties up to 175°C. A correlation between the microstructures, creep and BLR results reveal that the formation of a ternary CaMgSi phase is responsible for the improved elevated temperature behavior.

Any new Mg-alloys for the power train application in the automotive industry should have better elevated temperature mechanical and corrosion properties than the traditional AZ91 magnesium alloy. The price of AZ-Mg alloy modified with Ca and Sr, which can have adequate properties suitable for its service conditions, is expected to be comparable to that of AZ91 alloy and cheaper than AE42 alloy. The formation of thermally stable intermetallics, which are necessary for the improvement of creep properties, makes it a promising candidate for high temperature applications. This work investigates the mechanical and corrosion properties of AZ-Mg alloy modified with (Ca, Sr) in comparison with those of AZ91; the work included bolt load retention (BLR) and ageing behaviour. The aim is to give a preliminary evaluation of the overall performance of this modified AZ alloy. It is found that this alloy has a superior BLR property compared to AZ91 alloy with a good corrosion resistance.