Process for manufacturing aluminum alloys and aluminium castings

Abstract

A process for manufacturing parts made of aluminum cast or aluminum alloy cast in a mold, which includes after casting, removing from the mold the part which constitutes the cast preform while still hot, and placing it between two halves of a die that defines a cavity having dimensions that are slightly less than those of the mold, forcing said two halves together in order to exert a combined in-depth impact forging and surface hardening effect on the casting placed between the two halves. The invention further includes the step of transferring the cast preform prior to the impact forging step at a temperature of about 400 to 500° C. to a furnace that ensures solution heat treatment for the aluminum alloy at its homogenization temperature.

1 . Process for manufacturing parts made of cast alloy, especially aluminium cast or aluminium alloy cast, in a mould and which comprise, after casting, removing from the mould the part which constitutes the cast preform which is still hot and placing it between two halves of a die that defines a cavity having dimensions that are slightly less than those of the mould, forcing the two halves together in order to exert a combined in-depth impact forging and surface hardening effect on said casting placed between the two halves, 
 Wherein    the original feature of the invention involves introducing an intermediate step between the foundry phase in which the cast preform is obtained and the forging phase, with the foundry phase involving casting the liquid aluminium at a temperature of 750° C. in a mould that is heated and kept at a temperature or roughly 400° C., the aluminium cast in the mould in the liquid state tending to cool until it reaches the temperature of the mould of roughly 400° C., thereby producing a preform that is then transferred to a furnace preheated to a temperature of roughly 540° C. in order to ensure solution heat treatment of said cast preform at said temperature of 540° C.,    transferring the treated preform heated to a die that defines a cavity having dimensions that are slightly less than those of the mould, the two halves of the die being forced together in order to exert an impact forging/die forging force in order to obtain the finished rough forging,    cooling the forging casting thus obtained at room temperature or accelerated cooling or cooling by quench hardening.    
     
     
         2 . Process as claimed in  claim 1 , characterised in that high temperature homogenization time correspond to the heating time in order to obtain the same part criteria varies and takes approximately one hour.  
     
     
         3 . Process as claimed in  claim 1 , characterised in that the three operations of casting, heat treatment in a tunnel furnace at 540° C. and then impact forging are supplemented by a fourth operating phase after impact forging which involves carrying out an additional solution heat treatment operation on the part in another tunnel furnace at approximately 540° C. for a period of about 1 hour, 
 and in that this fourth operation is followed by a fifth quench hardening operation.  
 
     
     
         4 . Process as claimed in  claim 1 , characterised in that the parts obtained after the final operation and the second quench undergo natural ageing.  
     
     
         5 . Process as claimed in  claim 3 , characterised in that the parts obtained after the final operation and the second quench undergo natural ageing.