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Claim 1

A METHOD OF MAKING AN ALUMINUM-CLAD CORE STRUCTURE HAVING A CORE MATERIAL INCLUDING A METAL SELECTED FROM THE CLASS CONSISTING OF ALKALINE EARTH METALS AND ALKALINE EARTH METAL ALLOYS AND CHARACTERIZED IN BEING REACTIVE WITH THE ORDINARY ATMOSPHERE, AND COMPRISING THE OPERATIONS OF HEATING SAID MATERIAL TO A TEMPERATURE BELOW THE MELTING POINT THEREOF AND IN AN ATMOSPHERE AT BELOW ORDINARY ATMOSPHERIC PRESSURE WHEREBY SAID MATERIAL IS SUBSTANTIALLY DEGASSED, FURTHER HEATING SAID MATERIAL IN AN ATMOSPHERE OF AN INERT GAS AT A PRESSURE AT LEAST AS HIGH AS THAT OF THE VAPOR PRESSURE OF SAID MATERIAL AND TO A TEMPERATURE SUFFICIENT TO MELT SAID MATERIAL WHEREBY SAID MATERIAL IS MELTED WHILE EVAPORATION OF SAID MATERIAL IS REDUCED, STILL FURTHER HEATING SAID MATERIAL IN SAID LAST NAMED ATMOSPHERE FOR ACHIEVING A POURING TEMPERATURE OF SAID MATERIAL WHICH IS ABOVE THE MELTING POINT THEREOF, POURING SAID MATERIAL IN AN INERT GAS AT SAID LAST NAMED PRESSURE INTO AN ALUMINUM CONTAINER WHICH HAS A MELTING POINT BELOW SAID MELTING POINT WHILE DRAWING HEAT FROM THE INSIDE SURFACE OF SAID CONTAINER THROUGH SAID CONTAINER TO MAINTAIN SAID INSIDE SURFACE AT A TEMPERATURE BELOW THE MELTING POINT THEREOF AND THEREBY PREVENTING ANY ALLOYING BETWEEN SAID CORE MATERIAL AND SAID CONTAINER, COOLING SAID MATERIAL IN AN INERT GAS TO A TEMPERATURE BELOW THE MELTING POINT OF SAID CONTAINER, AND MECHANICALLY WORKING SAID CONTAINER TO REMOVE ANY GASES ENTRAPPED THEREIN WITH SAID CORE MATERIAL AND TO CLOSE AN OPENING IN SAID CONTAINER, WHEREBY AN ALUMINUM-CLAD CORE STRUCTURE IS PROVIDED HAVING A SUBSTANTIAL FREEDOM FROM ENTRAPPED GASES.