Strengthening Mechanisms in the Aged ۲۰۲۴ and ۷۰۷۵ Aluminium Alloys

Aluminum ۲۰۲۴ and ۷۰۷۵ alloys which are widely used in aerospace and marine applications were chosen to investigate their strengthening mechanisms. Using differential thermal analysis (DIA), metallography and tension tests, the best solutionizing conditions were determined to be ۵۰۰±۵°C and ۲ hours for ۲۰۲۴ and ۴۸۰?±۵°C and ۱ hour for ۷۰۷۵ alloy. Aging was performed in the range of ۱۰۰ to ۲۰۰°C for various times. It was concluded that the maximum strength in ۲۰۲۴ alloy was developed at l۸۰-۱۹۰°C after ۱۰ hours and in ۷۰۷۵ alloy at ۱۲۰°C for ۲۸ hours. In order to determine the strengthening mechanisms in these alloys qualitatively, the T۸ treatment (cold work plus aging) was carried out. The results show an increase in the mechanical strength of ۲۰۲۴ alloy whereas the ۷۰۷۵ alloy was not affected appreciably by cold working. It can be concluded that the strengthening mechanism in the ۲۰۲۴ alloy is due to the stress field around the precipitates, whereas in the ۷۰۷۵ alloy it is due to chemical strengthening.