Aluminum fluoride conversion coating has been a popular lubricant for aluminum cold forging. However, it has considerable environmental risks and problems of cost. A double-layer environmentally friendly solid lubricant has been developed as a substitute. The lubricant film was constructed of undercoat and overcoat layers. The authors applied it to three kinds of aluminum alloys. It was evaluated by a friction test based on spline extrusion. The differences in the lubrication performance caused by the season, flow stress, surface-roughing preprocesses, and undercoat film thickness were investigated. It showed better performance in rainy season, but performance was worse in winter. When it was applied to a harder material, the lubrication performance was improved by using a thicker undercoat and an appropriate preprocess. In contrast, when it was applied to a softer material, the undercoat thickness, and preprocess did not affect to the lubricating ability.
