May/June_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 | M A Y / J U N E 2 0 1 8 2 5 failed to make the switch for its 1928 Model A, but the drive toward steel bod- ies was unstoppable. Soon both Gener- al Motors and Ford Motor offered steel bodies, although the fabric roof en- dured a bit longer. In 1935, Inland Steel Co. in the U.S. commissioned a 76-in. wide mill and modern auto body sheet steel was on its way. ALUMINUM SHEET MAKES A COMEBACK At this point, aluminum sheet was no longer competitive, lacking the low cost combination of strength, ductility, and coil widths achievable with steel. Instead, aluminum sheet development was driven by the burgeoning commer- cial airplane market opened by Duralu- min. Unfortunately, the resultant 2 xxx heat-treatable alloys were not applica- ble to the auto industry; they are very strong after heat treatment but lack formability, and while formable enough in T4 temper, they lack the required strength. The bake temperatures of the enamel paints used at the time were too low, so there was no possibility to age harden after forming without add- ing a prohibitively expensive additional heat treating step. Further, the existing resistance spot welding techniques re- quired a full chemical cleaning of the sheet, which added another step and cost to an aluminum sheet solution. However, aluminum sheet tech- nology improved rapidly. In 1927, Al- coa cast the first 450 kg (1000 lb) water cooled ingot, and in 1928 successful- ly rolled an ingot two-and-a-half times that size. These were the early steps of direct chill (DC) casting, which greatly improved the economics of aluminum wrought product production by en- abling much larger ingots than possible with the existing tilt molds, with high- er quality and less waste during casting and rolling [9] . DC casting also enabled casting of richer alloys, like the new Al- Mg alloys (5 xxx ), which were introduced in themid-1930s inboth theU.S. and Eu- rope. These alloys offered both higher strength and good formability as well as corrosion resistance. Sheet made from these non-heat-treatable alloys could now be used in stamping applications, including light structural applications in automotive parts. The war build-up of the latter half of the decade result- ed in the appearance of all-aluminum fighters and bombers, further accel- erating advances in aluminum sheet technology in the U.S., Europe, and Ja- pan, where the first locally produced in- gots were made in 1934. Larger ingots drove the implementation of larger roll- ing mills, yielding improved quality and larger coils while lowering costs. The next steps toward an alumi- num mass-produced car occurred in France, where on November 2, 1934, the Société des Ingénieurs de l’Automo- bile offered a FF 200,000 prize in a com- petition to develop a lightweight, low cost, high efficiency two-seater [10] . Jean- Albert Grégoire, a 35-year-old indepen- dent automotive engineer, believed he had the solution, which he offered in 1935 after joining forces with Les Alu- minium Français (LAF) and the Foundry Montupet. His solution was to replace the steel chassis and stamped steel un- derbody of a production Adler Trumpf Junior with a cast aluminum under- body. The prototype demonstrated the advantages of the concept: a more rigid structure that was also lighter and qui- eter than the donor vehicle. While he did not win the competition, he attract- ed the support of LAF, and in turn, the attention of the commercial director of Amilcar, a dying French carmaker com- pany with hopes of reviving its fortunes with a radical solution. Together they convinced Hotchkiss, Amilcar’s par- ent company, to pro- duce a small popular car. It entered produc- tion in 1937 as the Amil- car Compound, but only 681 were produ- ced before WWII inter- rupted production and the company shut down. WORLD WAR II CURTAILS AUTO PRODUCTION Germany invaded Belgium and the Neth- erlands on May 10, 1940, and Belgium surren- dered less than three weeks later. Paris was declared an open city on June 13, followed by the armistice on June 22, and the French occupation began. With gasoline severly rationed, Grégoire contracted with the Compa- nie Générale de l’Électricité to de- velop and produce an aluminum battery electric vehicle (BEV) in late 1940, and 200 were produced between 1942 and 1944. LAF became interest- ed in promoting the concept of an alu- minum car, and on January 10, 1941, it contracted Grégoire to build four run- ning prototypes to be known as AFG, for Aluminium Français-Grégoire. While he missed the July deadline, the first pro- totype chassis was ready in September, and the first bodied vehicle was on the road in July 1942. Grégoire not only en- gineered and built a new chassis and suspension system, but he also built a new engine and a new transmission, all featuring aluminum castings. By early 1943, the four prototypes were offered for testing to the major French car man- ufacturers, Renault, Peugeot, Citroën, and Simca. However, the companies preferred to continue with their own in- house developments. On June 26, the president of LAF loaned one of the AFG prototypes to Panhard & Levassor (PL), known for its luxury cars. The compa- ny also manufactured a successful line of mid-size trucks, as well as light ar- mored vehicles for the military. There was probably some earlier contact between LAF and PL, because 1937 Amilcar Compound. Courtesy of Wikimedia Commons/ dave_7.