Characteristics of Fluoride Based Conversion Coating Film on Al-Alloy for Metal Forming Applications

Abstract

During the process of cold forming of aluminum, the high pressure which is introduced on the die can result in high adhesion between the aluminum and the die surface. Therefore, it is necessary for the aluminum billet to be coated with a lubricant prior to forming, to reduce adhesion and to ease the flow of material in the die. There are several popular types of lubricant systems used in cold forging of aluminum. For severe deformation, conversion coating in conjunction with soap lubricant are commonly used. The conversion coatings include soap phosphates (PO4-soap), as well as soap aluminum fluoride (AlF-soap). Therefore, this work studied the performance of the AlF-soap system and compared it to the conventional PO4-soap system as tested on AA6063 aluminum. Ring compression tests and ball on disc tests were conducted to explore friction conditions and the thinning of the lubricant under several forming conditions. It was found that the quantity of metal soap layer of AlF-soap used affected the friction coefficient and the lubricant thinning under forming operation. The suitable coating weight of metal soap layer of AlF-soap for this experiment was found to be 2 g/m2. The friction coefficient of the PO4-soap system was 16.26% lower than the AlF-soap system. However, the amount of thinning of the AlF-soap film after ring compression tests was lower than that of PO4-soap film.