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An experiment to determine the effects of mill oil weight, phosphate coating type and weight, surface roughness, and blank wash on the formability of prephosphated galvannealed steel was conducted. Limiting dome height, limiting drawing ratio and draw bead simulator friction tests were run on bare galvannealed and galvannealed coated with a conventional process phosphate and with three Dried-in-Place (DIP) phosphate products. Formability performance of both the conventional and DIP phosphate coated products was significantly better than that of oil-only coated galvannealed steel. Phosphate coating weights heavier than about 0.6 g/m2 per side did not significantly improve formability. The formability improvement from phosphate coating was about equal for the four products tested, with optimum oil weight for formability in the 1.3 to 1.9 g/m2 range. Surface roughness (within the testing range) and blank washing had no significant effects on formability.

A selection of commercially available chromium and chromium-free post phosphate rinses along with a deionized water rinse were evaluated over several zinc and zinc-alloy coated sheet steels. The test specimens were pretreated and electrocoated on-line in an automotive assembly plant. The effect of the rinse treatments on the cosmetic corrosion performance of the substrates, after 5 years of exposure in an outdoor scab corrosion test was determined. After this exposure none of the rinse treatments had performed better than deionized water rinse on zinc and zinc-iron coated sheet. The zinc-nickel coating showed improved scribe creepage when treated with the Cr+6/Cr+3 rinse. Data is provided comparing the concentration of the treatments used vs scribe creepage and chipping corrosion paint loss.

A comprehensive selection of automotive sheet steels were exposed in an outdoor scab corrosion test to provide a base-line of cosmetic corrosion performance. Eighteen different coated sheet steels along with CRS as a control were processed using two commercially available zinc phosphate chemistries. The phosphating was done using both immersion and spray phosphate processes in a laboratory and an automotive assembly plant. Scribe creepage results are reported for 5 years outdoor scab exposure. Comparisons of the scribe creepage behavior of CRS, zinc, and zinc alloy coatings and the effect of the phosphate treatment are provided. An estimate of 10 years field performance is made.

There is currently no widely accepted accelerated test used by the automotive industry to evaluate perforation (inside-out) corrosion. Historically, automotive companies have used Proving Ground evaluations of full vehicles to assess perforation corrosion. Such tests are expensive, do not lend themselves to comparative testing of a large matrix of materials or processes, and are not available to supplier companies. The Perforation Subcommittee of SAE ACAP Division 3 has initiated a project to obtain perforation corrosion data from on-vehicle exposures that will lead to the development of appropriate laboratory perforation corrosion tests. The first phase is the development of a test specimen and methods to evaluate corrosion on this specimen. The proposed specimen is a two-panel assembly having an un-painted test area separated by a gap distance of .25 mm.

In order to clarify the effect of design and materials of the hem as well as the climatic factors on perforation corrosion of the automobile doors, field car and laboratory investigation has been carried out Field car investigation revealed that corrosion of the hem can be minimized by using two side galvanized steel plus adhesives. The ratio of wet/dry environment was evaluated in laboratory on hemmed sample, and it was found that the design of the hem in conjunction with the various wet/dry ratio affected the corrosion rate differently.

Various steel substrates which were processed under different pretreatment conditions and coated with automotive paint systems, were investigated by electrochemical impedance spectroscopy (EIS). The impedances of damaged and undamaged organic coatings on cold rolled steel were measured in an aqueous sodium chloride solution. These results were compared with two conventional accelerated exposure tests, the High Temperature Chipping Corrosion Test (HTCCT), and the modified Volvo outdoor exposure test. The chipped organic coatings on cold rolled steel, electrogalvanized zinc, ZnFe electrogalvanized, and ZnFe hot dip galvanized were then investigated by EIS. An inhomogeneous three-dimensional surface model was used to analyze the EIS data and characterize the corrosion protection of the paint/phosphate/metal system. The fraction of the total test area which had undergone paint delamination and corrosion was calculated from the model results.

Direct comparisons of scribe creepage measurements were made between accelerated cosmetic corrosion tests and 2 year field exposure results from St. John's Newfoundland. Test acceleration rates were calculated for each of the ten AISI materials and their correlation with the field exposure was determined. Comparisons are made using twelve different cyclic corrosion tests, 3 laboratory environmental; 2 highway trailer and 3 proving grounds tests. All of the tests that were investigated accelerated the zinc-coated steels at a higher rate than cold rolled steel. The range of the higher acceleration was from 1.4 up to 110 times the field rate. The most favorable tests were the two outdoor scab tests at sea coastal sites, two proving grounds test cycles and a highway trailer test. The laboratory test with the most favorable response was the GM 9450 P, Method B cyclic corrosion test.