Alcoa Davenport quench-and-temper failure

A plugged water jet on the world's largest aluminum rolling mill at Davenport produced under-quenched streaks in plate that had already been machined onto flying Boeing aircraft. Government-Alcoa-airlines partnership developed an electrical-resistivity NDT probe to find affected wings in service.

To give you an example: there's a specification going back to the 1970s that you have to quench and temper your high-strength aluminum alloys. It's not the same as martensite — when we go through aluminum welding we'll talk about how you treat aluminum alloys that are quenched and tempered for different metallurgical reasons. You get higher strength, but you get precipitation hardening, not martensite. There's one plant in the United States, the Davenport Iowa works of Alcoa, that has the world's largest rolling mill. That's where they roll all the plate — four-and-a-half-inch-thick, six-inch plate, huge plate — for Boeing and a number of aircraft companies. If you're going to build a huge aircraft, you have to buy from Alcoa at this plant. To quench these big plates, they have a series of water jets. The hot plate goes under this shower of water jets, gets quenched, and is later tempered.