Aluminum Alloy 7178 is a very strong zinc-aluminum alloy. Its excellent strength is due in part to its composition: 88.1% aluminum, 6.8% zinc, 2.7% magnesium, 2.0% copper, and 0.26% chromium. Aluminum Alloy 7178 can be easily altered by a number of metalworking processes, including heat treating, machining, and welding, particularly resistance welding. Continental Steel & Tube Company stocks extruded Aluminum Alloy 7178 in angle bars of a variety of dimensions, typically at ninety degrees.