July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 1 8 2 3 that it took place on “as is” surfaces, di- rectly from stamping and without any intermediary cleaning. Although alumi- num spot welding was invented during WWII, it was based on the assumption of a cleaned surface. Introducing a cleaning requirement was a nonstarter in the automotive world, so automak- ers had to look to alternatives until a more robust and tolerant spot welding process became available. Mechanical clinches were available, but that meant the outer and the inner could not be hemmed together, so they needed to be joined on downstanding flanges or on pinch flanges hidden under moldings. Both solutions imposed styling limita- tions, causing aluminum sheet to lose friends in all levels of the car develop- ment process. From accountants and design studios to product engineers and stampers, all bemoaned the use of aluminum and clamored for something more accommodating, more like steel. However, cars needed to lose weight and the hood was a good place to start: The part was large and alumi- num resulted in 50% weight savings, more than 25 lb on a car of that period. So development continued. By 1974, Al- coa had registered a pair of new, scrap compatible alloys: 6010 for outer skins and 6009 for inners. Bothwere designed to offer enhanced properties compared to 2036 with a slightly better age hard- ening response in the E-coat baking cycle, allowing them to overcome a slightly lower incoming strength. That lower incoming strength was actually an asset in the fight against springback, and GM would adopt the pair for their first mass produced parts. Ford did not see significant advantages and stuck with 2036. By the time of the oil crisis, the U.S. aluminum industry was only partially ready for the production of high qual- ity automotive sheet. The first prob- lem was coil width, as most standard finished coil (after trim) widths at that time were 48 or 60 in. Automakers tar- geted hoods as the first part to switch to aluminum, and the hoods on the large cars of that time required widths of up to 1800 mm (72 in.). The problem did not lie with ingot sizes or rolling capa- bilities; these had been upgraded due to aerospace and can stock requirements. The issues with production of automo- tive sheet were mainly related to the continuous heat treatment process. The thin sheet (~1 mm) and wide width dictated a continuous coil process. Heat treatment of individual sheets, as per- formed during WWII, would have been a production nightmare for sheet han- dling and surface quality. Continuous annealing, which did not necessarily re- quire a rapid quench, was available in locations such as Alcoa-Tennessee and Alcan-Kingston by the early 1960s. Most of the production was for non-heat- treated alloys, although Alcoa-Tennes- see did produce some 6xxx canoe sheet with an air quench around this time. Alcoa-Davenportcommissionedan 86-in.-wide continuous heat treatment line in 1969 for aerospace sheet. Sever- al important differences made for dif- ficulties in auto sheet production. The 2xxx or 7xxx aircraft sheet was thick- er and needed a strong water quench. Similar quenches for softer, thinner (~1 mm) 6xxx sheet caused problems with distortion and surface quality. Sep- arate leveling to meet stringent flatness requirements was sometimes required. All of this added to low productivity (T/hour), low volume, and much low- er margins compared to the aerospace sheet produced on the same equip- ment. This made early auto sheet pro- duction unpopular at times with plant management. Nevertheless, the 86-in. line at Davenport would produce the bulk of Alcoa’s heat-treated auto sheet for more than 15 years. For the 1978 model year, both GM and Ford launched the first mod- ern American vehicles with alumi- num sheet: GM was ahead of Ford and launched aluminum hoods on four models, with two adding an alumi- num trunk lid. Ford was content to launch one hood on their new Lincoln Versailles. Both the automotive and alumi- num industries had learned a lot in the preceding eight years, with the early enthusiasm for automotive aluminum sheet tempered by the harsh realities of production. For now, aluminum sheet was viewed simultaneously as a low margin, low productivity product by the mills, and as a constraining, expensive, and low productivity material by the automakers. It was more of a shotgun wedding than a love affair. ~AM&P Note: Look for the third part of this article series in the September issue of AM&P. For more information: Laurent Chap- puis, president, Light Metal Consultants LLC, 8600 Church Rd., Grosse Ile, MI 48138, lbchappuis@icloud.com . Acknowledgments The authors thank R.E. Ray, W.B. Stever- son, R.J. Kegarise, and S.L. Shelby, all retired Alcoa employees, for their input and insight regarding the history of au- tomotive aluminum. 1980 Lincoln Versailles. Courtesy of Wikimedia Commons/55allegro.