Question

Question 33. Heat treatments are often performed on metal alloys in order to control their properties. (a) Briefly describe how heat treatments can affect the strength and ductility of metals. (2 Marks) (b) Wrought aluminium alloys often contain alloy constituents to improve various properties. 6xxx series aluminium alloys contain Magnesium and Silicon, which if present in appropriate concentrations, can form a hard intermetallic phase Mg2Si in the microstructure. Describe a suitable precipitation hardening heat treatment process for containing 0.5% Mg2Si phase. In your answer include a thorough description of each of the process steps (including temperatures) and indicate what is happening at the microstructural level in each of these steps. A Quasi-binary section showing the solid solubility of Mg,Si in aluminium for the Al-Mg-Si ternary is provided below. (4 Marks) an alloy 700 1200 Al liquid 595 C (1103 F) 600 1100 Al solid 1,85 solution 1000 500 900 800 400 700 600 300 Mg2Si Al+ / 500 200 400 300 100 200 100 Al 0.5 1,5 2 2,5 3 M Si 3.5 Temperature, "C 30 T Temperature, F

Answer 1

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A1-Mg Al Sod Sotitn A1