An aluminum alloy of age-hardening type indispensably containing copper, magnesium and silicon, being optionally added thereto traces of any one or more than one element selected from vanadium, manganese, chromium, zirconium and titanium.A sheet or strip made from said alloy ingot, being submitted to solution treatment followed by precipitation process can improve forming properties, such as tensile strength, LDR and/or earing ratio, and be free from stretcher-strain marks.Said sheet or strip maintains high strength particularly when it is submitted to baking i.e. high temperature curing of paint coated thereon.