The creep behavior of Mn-modified Al–Si–Mg–Cu–Mo alloy intended for diesel engine applications was investigated. Al–7Si–0.3Mg–0.5Cu–0.15Mn–0.3Mo (MG3-1) and Al–7Si–0.3Mg–0.5Cu–0.5Mn–0.3Mo (MG4-1) alloys presented apparent activation energies for creep of 203 kJ mol−1 and 249 kJ mol−1, respectively. TEM results indicated that in both alloys, dynamic recovery was the rate-governing mechanism and sub-grains were associated with Si phase particles. MG4-1 had finer sub-grains and a lower creep rate than the MG3-1. In the MG3-1 alloy, the effective diffusion coefficient, \({D}_{\text{eff}},\) of dynamic recovery and the apparent activation energy for creep, \({Q}_{a},\) agreed with the coefficient and the activation energy of Mn diffusion in aluminum, respectively. Si diffusion played a key role in governing the creep rate of MG4-1 where Si diffusion was limited due to the stability of the α-Al(Fe,Mn,Mo)Si dispersoids; this limited the coarsening of Si particles and reduced their effect in initiating recovery. Differences in the size and coherency of α-Al(Fe,Mn,Mo)Si dispersoids were observed and were attributed to the higher thermal stability and lower coarsening rate of the intermetallics at the solutionizing temperature. Coherent shearable α-Al(Fe,Mn,Mo)Si dispersoids did not provide sub-grain boundary pining in MG3-1. Coherent non-shearable α-Al(Fe,Mn,Mo)Si dispersoids in the size range of 6 nm pinned sub-grain boundaries in MG4-1. The apparent activation energy for creep in MG4-1 had contributions from the activation energy for Si diffusion in aluminum, pipe diffusion that governs sub-grain boundary migration, and Zener pinning by non-shearable coherent dispersoids.
