STRENGTHENING MECHANISMS IN A TWIN ROLL CAST AA8006 ALLOY

摘要

A twin roll cast AA8006 aluminium alloy (A11.8%Fe0.8%Mn0.2%Si) containing a high volume fraction of second phase particles has been investigated. Cold rolling to a strain e=2 results in a nearly equiaxed fine-grained structure, with the particles mainly situated on the subgrain-boundaries. Zener-drag causes recrystallisation to be delayed, and the alloy softens almost completely due to recovery. This gives a material with an excellent combination of strength and ductility. The coarsening of the particles and the growth of subgrains have been followed in detail in TEM. Tension tests have shown that the flow stress varies linearly with the inverse subgrain size (αapprox=2.9). One of the objectives of this work has been to seperate the strengthening mechanisms in the alloy, i.e. seperate the contributions due to particles and subgrain boundaries. By subjecting specimens back-annealed to different levels of strength (different subgrain sizes) to a flash-annealing treatment at high temperatures, they will recrystallise. In the recrystallised material there will only be a contribution from the second phase particles and solid solution.