1985 automotive galvanized steel spot-weld electrode failure

Post-1972 oil embargo, automakers shifted to galvanized steel for rust warranties. Zinc alloyed with copper electrode tips, creating high-resistance interface. Ford spec demanded 2,000 welds; plants getting 100–200. Used as worked example for Fourier number (third-of-a-second weld vs. 2–3 second cycle) and then for Laplace-equation current concentration at electrode tip angle (15° vs. 45°).

Student: [Suggests cooling happens between welds rather than during.]

Yes, you've got the cycle between welds, and you definitely will cool — there's like two or three seconds between welds. To give you a real-world example, and one of the ways I've used this. About 1985, they were welding galvanized steel in the automotive industry. Terrible problems. They used to weld non-zinc-coated steels, because they didn't care if your car rusted out in three years — you'd have to buy a new one. But after the 1972 oil embargo, the goal was to have cars with no rust for seven years. They started giving warranties to that effect and were losing their shirts. So they started galvanizing the steel, putting a zinc coating on as a sacrificial anode.