Method for heat treatment of precipitation hardening Al allot

Abstract

There is provided a precipitation hardening Al alloy in which an average area of eutectic structures existing in the Al alloy is less than 4 μm 2 . This Al alloy contains 6.5 to 7.5% by mass of Si, 0.36% by mass or less of Mg and 20 to 70 ppm of Sr, and is preferably used as a vehicle wheel. In heat treatment method of the precipitation hardening Al alloy, a work piece is subjected to 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 the solution treatment and aging treatment is carried out at temperatures from 150° C. or more to less than 200° C. The precipitation hardening Al alloy to be obtained has well-balanced three mechanical properties of tensile strength, yield strength, and elongation, and is also excellent in fatigue strength.

1 - 4 . (canceled)  
     
     
         5 . A heat treatment method of a precipitation hardening Al alloy which comprises; subjecting a work piece comprising a precipitation hardening Al alloy containing 6.5 to 7.5 by mass % of Si, and 0.36 by mass % or less of Mg 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, temperature raising to said solution treatment temperature is carried out within 30 minutes, a maintaining time further at said solution treatment temperature is 25 minutes to 3 hours, 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 . (canceled)  
     
     
         7 . The heat treatment method according to  claim 5 , wherein said solution treatment temperature is 540 to 550° C.  
     
     
         8 . The heat treatment method according to  claim 5 , wherein said fluidized bed is formed by direct blowing of hot air.  
     
     
         9 . The heat treatment method according to  claim 7 , wherein said fluidized bed is formed by direct blowing of hot air.