In the present study, AA6082 aluminium is deposited onto AISI 4140 steel substrates via friction surfacing (FS). Aiming to understand the influence of substrate surface for the bonding mechanism during the plasticising as well as the deposition phase, three different surface topographies have been manufactured via grinding and machining. Subsequently, FS process parameter dependencies on the deposits have been investigated. The resulting optical appearance, geometry and microstructure of the deposits have been studied. A deeper surface topography was found to facilitate plasticising and therefore FS layer deposition. Defect-free layer-to-substrate (LTS) joints have been generated for all topographies showing a fine-grained recrystallized microstructure as well as flow lines in the AA6082 deposits following closely the substrate surface topography, whereas no metallurgical changes in the AISI4140 substrates have been detected. At the LTS interfaces, a correlation of flow lines to an increased occurrence of high angle grain boundaries is identified. Appearance, geometries and grain size ratios of the AA6082 deposits show a dependency on substrate surface topography. Although complete bonding was achieved in the LTS joints, no distinct diffusion zone or interfacial mixing was observed. Mechanical interlocking on the micro scale was detected only for the samples with ground substrate surfaces.