The invention relates to projection welding of a second metal sheet above a first metal sheet (50), wherein the first metal sheet is of a non-ferrous metal or metal alloy having as main component aluminum or magnesium, wherein the first metal sheet comprises an elongate projection that locally extends above the main upper surface of the first metal sheet to come into contact with the main lower surface of the second metal sheet, wherein the projection comprises an upper surface having a convex first section (65) with a first radius (R1) that defines in its middle the top height of the upper surface with respect to the main upper surface of the first metal sheet, and a convex second section (64) with a second radius (R2) along both elongate sides that merge into the first section, wherein the first radius is larger than the second radius.