[en] We present a numerical study of the mixing of an FeLu alloy due to bombardment by 5 keV Ar⁺ and Xe⁺ ions. A dual approach is used to calculate the evolution of concentration profiles in a multi-component target with the fluence of irradiating ions. In a first step, Monte Carlo simulation is used to calculate the atomic relocation in a collision cascade set up by the bombarding ion. In a second step, the change of the concentration profiles due to atomic relocation is calculated using a finite-difference scheme. We check the numerical results using a diffusion approximation to the underlying evolution equations, and find good agreement. The approximation shows that the concentration evolution can be determined analytically from the preferential relocation of each species over the average relocation and the mean surface recession speed. For the FeLu system, we find that by varying one or several of the model parameters in our simulation - like the cutoff of the potential, or the displacement threshold - the preferential relocation, and hence the steady-state profiles, are changed. These changes can be understood qualitatively in terms of available analytical models. We compare with published results on this system, and discuss the discrepancies found. (orig.)