6061 Al alloy (1% Mg & 0.6 % Si major alloying elements) typically derives its strength primarily...
Question:
6061 Al alloy (1% Mg & 0.6 % Si major alloying elements) typically derives its strength primarily from precipitation hardening, but can also exploit solid solution strengthening under certain processing conditions. The yield strength of this alloy after solutionizing and quenching is 150 MPa. The strength can be increased to 250 MPa after aging for 1 hr at 230°C, and it is reasonable to assume that the solute has been completely depleted from the matrix under these conditions. Severe overaging reduces strength to 75 MPa, and it is reasonable to assume that coarsening under these conditions results in very widely spaced precipitates. Based on these facts:
a. What is the primary strengthening mechanism operative in the solutionized and quenched alloy and what is the magnitude of strengthening, Δσ, produced by this mechanism?
b. What is the primary strengthening mechanism operative in the aged alloy and what is the magnitude of strengthening, Δσ, produced by this mechanism? You should give brief rationale for each answer.
