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A new 5xxx-series aluminum alloy for auto body sheet is described. The new alloy GZ42 which is of Al-Mg-Zn-Cu system was developed to obtain excellent tensile ductility and formability. The most prominent characteristic of the new alloy is its excellent press formability over the other aluminum alloys for auto body sheet. Technical data is presented and discussed.

Extensive work was conducted to develop a corrosion resistant brazing sheet alloy and to apply it to a drawn cup type evaporator in automotive air conditioning system. The items to be investigated included the influence of chemical composition of the core alloy on corrosion resistance, suppression of erosion during the brazing cycle, and enhancement of the brazing sheet formability. Additional investigation was conducted to develop a new corrosion test method on the basis of better understanding of the mechanism of corrosion in the field and to evaluate the corrosion resistance of a evaporator fabricated from the new alloy. This paper, as Part 1, describes the results of alloy development from the metallurgical and electrochemical point of view.

A highly corrosion resistant drawn cup type evaporator was developed. During the development of this evaporator, the corrosion characteristics of evaporators in the field were examined in detail. Profound understanding of the corrosion mechanism led to the development of a new, unique, corrosion test method which simulates the actual evaporator field service environment. The main factors involved in increasing the corrosion resistance of the brazing sheet are (1) reduction of iron and silicon content in the core alloy and, (2) addition of titanium to the core alloy. In the present alloy, titanium content varies lamellarly through the thickness of the core alloy. Regions of high titanium content have a more cathodic potential, thus causing corrosion to proceed along the low titanium content lamellae. Consequently, the reduced iron and silicon contents, and the titanium addition, have the net effect of reducing the pitting corrosion rate.

The sacrificial anodic effect of Al-Zn alloy reduces markedly in aluminium heat exchanger as car air-conditioner manufactured by vacuum brazing conventionally used, as zinc elements preferentially evaporate in vacuum-heating. It was found that Al-Sn alloy had superior electrochemical characteristics than Al-Zn alloy (AA7072) as the sacrificial anodic material used in vacuum brzing. According to many experimental results, the new brazing sheet-fin with Al-Mn-Sn alloy core metal has been developed. This fin has favorable formability and prominent sacrificial anodic effect. Therefore, this fin is excellent material for car air-conditioner manufactured by vacuum brazing.