Performance of Coatings for Underbody Structural Components 2001-01-0363

The Auto/Steel Partnership established the Light Truck Frame Project Group in 1996 with two objectives: (a) to develop materials, design and fabrication knowledge that would enable the frames on North American OEM (original equipment manufacturer) light trucks to be reduced in weight, and (b) to improve corrosion resistance of frames on these vehicles, thereby allowing a reduction in the thickness of the components and a reduction in frame weight. To address the issues relating to corrosion, a subgroup of the Light Truck Frame Project Group was formed. The group comprised representatives from the North American automotive companies, test laboratories, frame manufacturers, and steel producers. As part of a comprehensive test program, the Corrosion Subgroup has completed tests on frame coatings. Using coated panels of a low carbon hot rolled and pickled steel sheet and two types of accelerated cyclic corrosion tests, seven frame coatings were tested for corrosion performance. The coatings included those that are currently in use for frames, such as the hot-melt waxes and E-coat, as well as those for potential future applications. One type of cyclic test was a proving ground corrosion trailer test (100 cycles) carried out on a test track at the General Motors Proving Ground test facility. The second type of cyclic test was based on the SAE J2334 laboratory corrosion test (80 cycles), modified to include a bake step at an elevated temperature (93°C, 121°C or 149°C) and an exposure to shot blast in the cycle. The modifications were designed to simulate corrosion under conditions of exposure of the coating to elevated temperatures from the automotive exhaust system and the damage to the coating by the road gravel impact. Both tests revealed differences in the performance of the frame coatings. Details of the test cycles, procedures for the evaluation of corrosion and the reasons for the performance differences are presented in this paper.