Magnesium and aluminum and their alloys are widely used for a variety of consumer products and in various industrial processes. Magnesium and aluminum are, however, subject to pitting corrosion and a variety of coatings have been applied to them to minimize such corrosion.
One particularly convenient method for providing corrosion protection for magnesium or aluminum is shown in U.S. Pat. No. 4,401,726. There, magnesium or aluminum was alloyed with a metal selected from the group consisting of Mo, W, Cr, V, Hf, Zr, Fe, B, Be, Ni, Co, Ta, Cb, Ti, Pd, Th, Rh, Re, Os, Ir, Pt, Cu, Au, and Mn. Such alloys were taught as providing corrosion protection and were formed by depositing a layer of alloying metal powder about 1.5 millimeters thick onto a magnesium or aluminum substrate and irradiating it with a laser beam. Irradiation was conducted in inert atmospheres to prevent oxidation of the metals. The laser radiation melted the alloying metal powder and a thin layer of the surface of the magnesium or aluminum substrate. The molten metals were mixed by thermal currents and maintained in a molten state for from about one to about two seconds or less. Then the mixture was solidified into crystalline microstructures.
Materials coated in this manner were thought not only to be corrosion resistant, but to be harder, stronger and more wear resistant than uncoated magnesium or aluminum.
Jain, Kulkarni and Sood ("Laser Treatment of Chromium Films on Aluminum at High Power Densities", Thin Solid Films, Volume 86 (1981) pages 1-9) irradiated Cr which had been deposited onto an aluminum substrate. The irradiation was conducted in the presence of air. However, they irradiated the coated substrate with a single laser pulse to determine its effect. They did not recognize that they may have formed mixed oxides nor did they recognize the highly beneficial corrosion resistance shown by such alloys.
It would be desirable to have magnesium and aluminum alloys which may be formed without the need for special inert atmospheres during alloying. It would also be desirable to have new alloys of magnesium and aluminum which are resistant to pitting corrosion.
It is an object of the present invention to provide alloys of magnesium or aluminum which are more resistant to pitting corrosion than unalloyed magnesium or aluminum.