GB745426A - A method of solid-phase bonding metals - Google Patents

Abstract

745,426. Jointing; working at specified temperatures. METALS & CONTROLS CORPORATION. March 24, 1952, No. 7589/52. Classes 83 (2) and 83 (4). [Also in Group XXIII] A method of solid-phase bonding metals comprises preparing the surfaces of the metals by eliminating any film which would act as a barrier to bonding, squeezing the prepared surfaces together and concomitantly effecting an increase in area thereof to form nucleal bonds 43, Fig. 2, the squeezing being carried out at a temperature below the minimum recrystallization temperature of the metal having the lowest recrystallization temperature, and thereafter subjecting the composite material to heat treatment to cause the nucleal bonds to enlarge. The squeezing may be accomplished by rolling mills in which strips or sheets are bonded, drawing dies in which a tube is bonded to a rod or another tube; strand or impact extrusion presses; and upsetting where two rods of metal are forced together endwise. Fig. 1 illustrates the squeezing step performed by rolling. Metal strips 1 and 3 pass through a surface preparation apparatus 11 and then through a sweep chamber 13 where loose dust is removed. Redeposition of dust is prevented by keeping the prepared surfaces in contact until the strips reach the rolling mill which effects a reduction in the total thickness of the strips of more than 30 per cent. The surface preparation comprises two steps: removal of gross contaminants and removal of films, e.g. of natural oxide which approach molecular dimensions in thickness and which either resist ordinary cleaning methods or reform after such cleaning. This second step may be effected by abrasion, bright annealing or pickling followed by heating to a temperature high enough to decompose the film or transform it into one which will not resist the bonding process. Such heating may take place in a furnace with a protective atmosphere or, alternatively, a blast of heated air, infra-red heat, or high frequency induction heating may be used. Abrasion is preferably effected by wire brushing (see Group XXIII) for a period which is adjusted to generate sufficient surface heat to decompose the film without creating a fresh detrimental oxide film. A neutral or protective atmosphere may be used. The wire brushes are degreased and then heated to destroy residual contaminants while the contacting parts, such as guides, are cleaned by sanding. The final heat treatment, which transforms the nucleal bond into a substantially continuous one and brings the metals to a softer condition, may be carried out at temperatures above or below the recrystallization temperature of either or both metals, but it is preferred to use a temperature between the lowest recrystallization temperature and that at which brittle compounds or liquid-phase material would form in appreciable amount. The Specification includes a tabular statement of the preferred method of heat treatment, mill operation and surface preparation for different combinations of metals.