Aluminum alloy formed by precipitation hardening and method for heat treatment thereof

Abstract

An aluminum alloy formed by precipitation hardening in which the eutectic structure present therein has an average area less than 4 m?2. The alloy contains 6.5 to 7.5 wt. % silicon, up to 0.36 wt. % magnesium, and 20 to 70 ppm strontium and is suitable for use as a vehicle wheel. The method for heat treatment of the aluminum alloy formed by precipitation hardening comprises: conducting a solution treatment by causing the work piece to be present in a fluidized bed so that at least 60% of the silicon and/or magnesium forms a solid solution in an a phase; and conducting an aging treatment at a temperature not lower than 150° C. but lower than 200° C. The aluminum alloy thus obtained has well-balanced three mechanical properties, i.e., tensile strength, proof stress, and elongation, and has excellent fatigue strength.

1 . A precipitation hardening Al alloy, characterized in that an average area of eutectic structures existing in said Al alloy is less than 4 μm 2 .  
     
     
         2 . The precipitation hardening Al alloy according to  claim 1 , wherein said alloy contains 6.5 to 7.5% bymass of Si, 0.36% by mass or less of Mg.  
     
     
         3 . The precipitation hardening Al alloy according to  claim 1  or  2 , wherein said alloy contains 20 to 70 ppm of Sr.  
     
     
         4 . The precipitation hardening Al alloy according to any of  claims 1  to  3 , wherein said alloy is used as a vehicle wheel.  
     
     
         5 . A heat treatment method of a precipitation hardening Al alloy comprising; 
 subjecting a work piece comprising the precipitation hardening Al alloy to solution treatment, and then    subjecting the work piece to aging treatment, to improve mechanical properties of the work piece,    characterized in that said work piece is subjected to said solution treatment by being made to exist in a fluidized bed, and further a rate of solid solutions of Si and/or Mg into a phase is made to be 60% or more in said solution treatment and said aging treatment is carried out at temperatures from 150° C. or more to less than 200° C.    
     
     
         6 . The heat treatment method according to  claim 5 , wherein temperature raising to said solution treatment temperature is carried out within 30 minutes, and further a maintaining time at said solution treatment temperature is 25 minutes to 3 hours.  
     
     
         7 . The heat treatment method according to  claim 6 , wherein said solution treatment temperature is 540 to 550° C.  
     
     
         8 . The heat treatment method according to any of  claims 5  to  7 , wherein said fluidized bed is formed by direct blowing of hot air.