Patent GB-577986-A (GB)
Title: Improvements in or relating to the manufacture of composite metal articles
IPC: B23K1/00
Filed: 1943-04-28
Abstract: 577,986. Heat - treating alloys. ALEXANDER, W. O., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. April 28, 1943, No. 6698. [Class 72] [Also in Group XXII] In making composite articles having one or more of the component parts composed of an alloy or alloys, including plain carbon steel, amenable to heat treatment for improving their mechanical properties, the parts are assembled with an interpbsed layer of brazing or soldering metal or alloy and subjected to coincident joining and heat treatment within the temperature range required for the heat treatment, the joining being effected at a temperature above the lowest permissible heat treatment temperature and when flowing of the solder &c. under surface tension is complete the assembly is slowly cooled to the lowest permissible heat treatment temperature or an intermediate temperature at which the joint sets and the heat treatment is completed. An effective joint is thus produced without sacrificing the properties of the alloys. The heat treatment comprises solution or phase transition treatment at an elevated temperature or tempering or precipitation hardening at a lower temperature or successive joining operations at different stages of manufacture of an article may be carried out at the higher and lower of such heat treatment temperatures respectively. When joining is effected at a temperature within the solution treatment range, the parts are preferably maintained at such temperature for the shortest possible time by using forced air circulation in the furnace or salt bath heating or by a preliminary partial, solution treatment of the separate components before joining. Further, when joining is effected within the solution temperature range, the article, after the joint has set, may be cooled at a rate sufficient to ensure supersaturation to obtain an alloy in unstable or metastable equilibrium at a lower temperature cooling being effected by air, steam, water or a cooler salt bath. Jigs may be used to position the parts and to prevent distortion on cooling. The alloys may be copper, aluminium, magnesium and nickel base alloys and for joining at solution temperature range may include copper-chromium, copper-nickel-aluminium, copper-nickel-aluminium-zinc, copper-nickel-silicon, copper - beryllium, copper-nickel-tin, nickel-copper-aluminium, strain ageing mild steel and medium carbon steel and the bonding material in such cuses may consist of copper, silver, brasses, silver solders, phosphor - copper, phosphor - silver - copper, or aluminium-silicon. Alloys to be joined at the tempering range may include copper-beryllium, nickel-copper-aluminium, and strain ageing mild steel with a bonding material of silver solders or soft solders. For one example, two pieces of copper-chromium alloy containing 0.5 per cent of chromium may be joined by assembling with an interposed layer of silver 0.005" in thickness. The assembly is heated at 1000‹ C. for 15 minutes in a furnace containing a controlled atmosphere. After withdrawal and on solidification of the solder &c., the assembly is quenched in water. The assembly is then temper-hardened for four hours at 450‹ C. Dissimilar alloys may be joined of which one or both are amenable to heat treatment if the range of heat treatmenttemperatures is substantially the same for the respective alloys. Thus, copper-chromium alloy may be brazed to steel by a brazing medium of brass. The articles jointed may consist of heat-exchange devices such as cylinder-head inserts and secondary surface cooling systems for the cylinders of internal-combustion engines as described in Specification 554,236, [Group XXII], flare traps for aircraft engines and also intercoolers, and after coolers for internalcombustion engines and refrigerator parts, cooling systems for dairy appliances, radiator heaters and driers.