GB546779A - Improvements in or relating to metallic coatings and their application to the surfaces of magnesium and magnesium rich alloys - Google Patents

Abstract

546,779. Making compound sheets. BARKLIE, R. H. D., and LEWIS, A. Jan. 31, 1939, Nos. 3218 and 23128. [Classes 83 (ii) and 83 (iv)] Soldering.-In a process of joining metals, particularly for applying a non-corrosive coating or coatings of aluminium, nickel &c. to easily oxidizable metals such as magnesium or alloys thereof, a metal interlayer consisting of two or more metals such as zinc and cadmium or bismuth and cadmium, which when heated attain a pasty condition including small crystals and a liquid, is placed between the parts to be joined, is heated to bring it into such condition, and is then submitted to mechanical working such as rolling or forging to cause relative movement between the solid parts of the interlayer and the adjacent surfaces of the parts. The temperature is less than that required to soften the parts to be joined. The interlayer, which may be applied by electrolysis, spraying, brushing or dipping and may be applied either to the base metal or to the coating sheets, may consist of an alloy or superposed layers of two or more of the metals. When zinc or cadmium are used the proportion of zinc may vary from 1 to 4 parts and the cadmium from 4 to 1 parts. Non-corrosive sheets may be first decreased and then electrolytically coated with cadmium for 20 seconds in a bath and under a current capable of depositing <SP>1</SP>/ 2000 inch in one hour. The sheet is then coated with zinc for 40 seconds and then again with cadmium for 20 seconds. The magnesium plate and the two coated plates are then assembled between heavy steel slabs and heated in a muffle to 330‹ C. The assembly is then passed between rolls heated to 140 ‹ C. so that during this stage the temperature of the parts drops and passes through the range of temperature of optimum pasty condition so as to unite the parts. The assembly is now annealed by either heating below 400‹ C. to reduce formation of bond constituents in the layer at the junction of the aluminium &c. and magnesium and then work-hardening or precipitation hardening, or heating up to 400‹ C. so that partial oxidization of the interlayer occurs and prevents the formation of hard constituents in the layer. The assembly is then again rolled at 260‹ C. and is finally cold rolled. Adhesion may be improved by subsequently heating to 100‹ C. for four hours. The coating sheets may be applied by spraying on to the interlayer which is previously applied to the base metal. The edges of the parts may be protected by bending the edges of one sheet over those of the others or by applying channel shaped covering strips, or by spraying with metal or rubber. The article may consist of a number of main sheets each protected by covering sheets to form a multiple sheet.