AlSn films (20 wt.% Sn) with a thickness of 20 mu m were prepared by magnetron sputter deposition in an argon gas plasma. It has been found that the oxygen content in the argon gas during deposition strongly influences film properties and surface morphology. From 0.005% up to 0.02% oxygen the films show a uniform and fairly smooth surface characterized by a roughness (RZ) of 3-5 mu m. From 0.05 up to 0.15% oxygen numerous whiskers of different shape and dimensions appear on the film surface. The whisker growth leads to an increase of surface roughness with peak values around 25 mu m. Above 0.5% oxygen no whiskers can be found on the film surface, but the film morphology changes from a dense structure to a loosely bonded one built up by spherolitic crystals. The microhardness of the films increases from 95 to 155 HV (Vickers hardness) with increasing oxygen content. Increasing either substrate temperature (110-160 degrees C) or film thickness (2-50 mu m) increases the surface roughness from 2 to 25 mu m or from 2 to 65 mu m, respectively, whereas moderately low roughness (8 mu m) can be obtained at argon gas pressures above 1 Pa.