Sensitivity Analysis of Ageing Parameters on Properties of AZ91 Magnesium Alloy by Regression Method

In this article, the effects of the ageing temperature and the ageing time in the heat treatment have been investigated on the hardness and the microstructure of AZ91 and AZ91+1%RE magnesium alloys, using the sensitivity analysis with the Minitab software. For this purpose, 8 ageing treatments with different temperatures and times were performed on AZ91 and AZ91+1%RE magnesium alloys and then, results related to the Brinell hardness and the microstructure of the optical microscopy, were compared. Based on results of the sensitivity analysis, the influence of the ageing temperature on hardness increasing was more than the ageing time. Moreover, ageing at 215°C and 3 hours enhanced the hardness of the AZ91 magnesium alloy about 57% and ageing at 215°C and 5 hours increased the hardness of the AZ91+1%RE magnesium alloy about 47%. In addition, ageing converted a large part of continuous precipitations to needle-shaped precipitations on the alpha phase and also reduced the amount of precipitations around the Mg17Al12 phase in the microstructure of both alloys.