Solute-vacancy clustering in Al-Mg-Si alloys studied by muon spin relaxation technique

Zero-field muon spin relaxation experiments were carried out with Al-1.6%Mg₂Si, Al-0.5%Mg, and Al-0.5%Si alloys. Observed relaxation spectra were compared with the calculated relaxation functions based on the Monte Carlo simulation to extract the dipolar width (Δ), trapping (v_t ), and detrapping rates (v_d ), with the initially trapped muon fraction (P₀). The fitting analysis has elucidated that the muon trapping rates depended on the heat treatment and solute concentrations. The dissolved Mg in Al dominated the v_t at lower temperatures below 120 K, therefore the similar temperature variations of v_t were observed with the samples mixed with Mg. The v_t around 200 K remarkably reflected the heat treatment effect on the samples, and the largest v_t value was found with the sample annealed at 100°C among Al-1.6%Mg2Si alloys. The as-quenched Al-0.5%Si sample showed significant v_t values between 80 and 280 K relating with Si-vacancy clusters, but such clusters disappeared with the natural aged Al-0.5%Si sample.