Search Results

Filiform corrosion phenomenon and its prevention method for 5000 series aluminum alloy sheet have been investigated. The painted aluminum alloy sheets were subject significantly to filiform corrosion caused by formation of a mottled and coarse zinc phosphate film during chemical conversion process. On the other hand, galvanized aluminum alloy sheet showed an uniform and fine phosphate film in a brief time and the filiform corrosion resistance was improved markedly. The test results of press-forming and corrosion for the prototype engine hoods made of this newly developed galvanized sheets have revealed a good formability and an excellent filiform corrosion resistance.

This paper discusses a portion of a larger program on filiform corrosion concentrating on test methodologies and environmental mechanisms that contribute to filiform corrosion. It is organized into four sections, the first covers background of filiform corrosion, materials used in the study, and procedures for the sample preparation and testing. Following this, there are sections on outdoor testing, accelerated testing, and environmental parameters all of which include some procedural information, results and conclusions.

Increasing use of aluminum in automotive components has led to lower fuel consumption and enhanced performance of automotive designs. From a manufacturing standpoint, aluminum provides the additional advantage of utilizing same processes as steel. Performance and durability of painted aluminum cars, however, is dependent on proper optimization of process conditions. As part of an extensive study of factors influencing corrosion resistance of painted aluminum, the present study deals with the influence of pretreatment and coating variables and the interaction of alloy composition with zinc phosphate and electrocoat. Interfacial analysis of corrosion products indicates the relative influence of alloying elements on stability of the metal/phosphate/electrocoat interface. As a result, guidelines and recommendations on aluminum processing in an automotive manufacturing floor have been developed.

In order to simulate the perforation corrosion of an automobile, hem model samples made of various kinds of coated steel sheets were set inside of the door outer panel and the door was exposed in the open air with once a week 5% salt spraying. After two years, the model samples were disassembled for investigation. Perforation corrosion occurred most severely just above the lapped portion of outer and inner specimens. Red rust samples taken from the hem model and from a field vehicle run in Detroit did not show clear pearks of spectra by X-ray diffraction analysis, whearas the one formed by a conventional cyclic corrosion test showed peaks of Fe3O4. These facts indicate that this new test well simulates the corrosion environment of an actual automobile hem portion. Corrosion resistance of many kinds of coated steel sheets was studied by this new test method. Perforation depth became smaller as a coating weight of pure zinc electroplated steel sheet increased.

A thin organic coated steel sheet (HI-SUPER-DN) has been recently developed for automotive body panel applications. The steel sheet consists of a Zn-Ni alloy-plated layer, a chromate film and a thin organic coated layer, which is composed of colloidal silica, organic polymer and an organic additive. Corrosion resistance, formability of the coated layer, weidability and electropaintability of the steel sheet required for automotive body panel were studied. An increase in the colloidal silica in the organic coated layer improves corrosion resistance. However, the formability of the organic coated layer deteriorates with such as increase in the colloidal silica. We have optimized the ratio of colloidal silica to organic polymer so as to balance both the corrosion resistance and the formability of the organic coated layer. Futhermore, the bake-hardenability of the steel sheet was maintained by a relatively low temperature baking of the chromate film and the organic coated layer.

Amidst of the recent concerns on depletion of natural resources, a new heat resistant titanium alloy has been developed using the minimum amount of rare metals. Using Ti-811 as a basis and modifying the alloy composition to Ti-7Al-2Mo-0.2Si-0.15C-0.2Nb, the mechanical property, the creep resistance and the oxidation resistance at high temperatures are improved. At the same time, with the β transformation point shifted to a higher temperature, the hot formability is also improved. The newly developed alloy has made it possible to expand the application of titanium material to exhaust valves in reciprocating engines.

In the 1st generation Toyota "MIRAI" fuel cell stack, carbon protective surface coating is deposited after individual Ti bipolar plate being press-formed into the desired shape. Such a process has relatively low production speed, not ideal for large scale manufacturing. A new coating concept, consisting of a nanostructured composite layer of titanium oxide and carbon particles, was devised to enable the incorporation of both the surface treatment and the press processes into the roll-to-roll production line. The initial coating showed higher than expected contact resistance, of which the root cause was identified as nitrogen contamination during the annealing step that inhibited the formation of the composite film structure. Upon the implementation of a vacuum furnace chamber as the countermeasure, the issue was resolved, and the improved coating could meet all the requirements of productivity, conductivity, and durability for use in the newer generation of fuel cell stacks.