Abstract: Auto body roof comprising at least one steel part and a skin part made of aluminum alloy that is attached to the steel part before painting. The aluminum part comprises a sheet of the following composition: Si: 0.7-1.3, Fe<0.5, Cu: 0.5-1.1, Mn: 0.4-1.0, Mg: 0.6-1.2, Zn<0.7, Cr 0.25, Zr+Ti 0.20, other elements <0.05 each and <0.15 total, and the remainder aluminum. The aluminum part, after solution treatment, quenching and age-hardening for three weeks at room temperature, possesses a yield strength R0.2 of less than 170 MPa, and preferably 160 MPa.

Abstract: Auto body roof comprising at least one steel part and a skin part made of an aluminum alloy that is attached to the steel part before painting. The aluminum part comprises a sheet of the following composition: Si: 0.7-1.3, Fe<0.5, Cu: 0.5-1.1, Mn: 0.4-1.0, Mg: 0.6-1.2, Zn<0.7, Cr<0.25, Zr+Ti<0.20, other elements <0.05 each and <0.15 total, and the remainder aluminium. The aluminum part, after solution treatment, quenching and age-hardening for three weeks at room temperature, possesses a yield strength R0.2 of less than 170 MPa, and preferably 160 MPa.

Abstract: A method for surface treatment of sheets and strips of aluminum alloy to form a chemically altered layer. The sheet or strip is the product of a manufacturing process including a thermal treatment step followed by cooling in a liquid in which a chemical conversion is carried out using the cooling liquid. The cooling liquid preferably contains between 1 and 10% by weight of at least one salt of one at least of the metals Si, Ti, Zr, Ce, Mn, Mo and V. The invention is particularly applicable to sheets and strips which need a controlled oxide surface for the production of chassis components for the automobile industry for spot gluing or welding.