Method of forming a cast aluminium alloy

Abstract

Al—Si—Mg castings to provide enhanced mechanical properties for structural applications comprising (1) alloy optimisation with 8.5 to 12.5 wt. % Si, 0.46 to 1.0 wt. % Mg, 0.1 to 0.2 wt. % Ti, 0.05 to 0.25 wt. % Mn, 0.01 to 0.02 wt. % Sr, 0.004 to 0.1 wt. % B and other impurity elements of Cu, Fe, Zn each less than 0.15 wt. % and the balance of Al; (2) optimised melt treatment with appropriate melting, modification, degassing and grain refining; (3) appropriate type of grain refiner with optimised amount and method to add into the aluminium melt, and (4) optimised heat treatment process. When being utilized to make shape aluminium alloy castings with gravity casting process, the castings have been achieved the 0.2% offset yield strength of greater than 310 MPa, the ultimate tensile strength of greater than 365 MPa and the elongation of greater than 10%.

1 .- 11 . (canceled) 
     
     
         12 . An aluminium alloy comprising:
 From about 8.5 to about 12.5 wt. % Si;   from about 0.46 to about 1.0 wt. % Mg;   from about 0.1 to about 0.2 wt. % Ti;   from about 0.05 to about 0.25 wt. % Mn;   and less than about 0.05 wt. % Sn;   the balance being Al and incidental impurities.   
     
     
         13 . An aluminium alloy as claimed in  claim 12 , further comprising:
 grain refining additions of Ti, TiB2, AlB2, B, Be, Zr, Y, V, Nb, singly or in combination with one another in the range from about 0.001 to about 1.0 wt. %;   Na and Sr, singly or in combination, in the range of from about 0.001 to about 0.10 wt. %; and   P in the range from about 0.01 to about 0.30 wt. %.   
     
     
         14 . A method of forming a cast aluminium alloy, comprising the steps of:
 (i) providing an aluminium alloy comprising
 from about 8.5 to about 12.5 wt. % Si, 
 from about 0.46 to about 1.0 wt. % Mg, 
 up to about 0.2 wt. % Ti, 
 from about 0.05 to about 0.25 wt. % Mn, 
 from about 0.002 to about 0.04 wt. % Sr, 
 from about 0.001 to about 0.1 wt. % B 
 and other impurity elements of Cu, Fe, Zn, each at less than about 0.15 wt. % with the balance being Al and incidental impurities; 
   (ii) melting the alloy to yield an alloy melt;   (iii) degassing the alloy melt by introducing into the alloy melt a gas comprising at least one of nitrogen, argon, or chlorine, or a mixture thereof to reduce dissolved hydrogen in the melt to a level of less than about 0.7 mL/100 g alloy melt;   (iv) cleaning the alloy melt by adding about 25% Na2SiF6 and 75% C 2 Cl 6  refining agents in an amount from about 0.01 to about 0.8 wt. %;   (v) adding a grain refiner in the form of a TiB-containing master alloy, a B-containing master alloy, or an Al—B master alloy with a boron content up to about 0.1 wt. % B, to yield an alloy having a eutectic silicon phase;   (vi) refining and modifying the eutectic silicon phase by adding from about 0.002 to about 0.04 wt. % Sr in the form of an Al—Sr master alloy;   (vii) carrying out a solution heat treatment at a temperature from about 520° C. to about 545° C. for a time from about 2 h to about 12 h; and   (viii) carrying out an ageing heat treatment at a temperature from about 170° C. to about 200° C. for a time from about 2 h to about 8 h.   
     
     
         15 . A method as claimed in  claim 14 , wherein the alloy of step (i) comprises:
 from about 8.5 to about 10.0 wt. % Si,   from about 0.456 to about 0.65 wt. % Mg,   from about 0.1 to about 0.15 wt. % Ti,   less than about 0.15 wt. % Mn,   from about 0.008 to about 0.02 wt. % Sr,   from about 0.004 to about 0.04 wt. % B   and other impurity elements of Cu, Fe, Zn, each at less than about 0.15 wt. % and the balance of Al and incidental impurities   
     
     
         16 . A method as claimed in  claim 14 , wherein the dissolved hydrogen in step (iii) is reduced to a level of less than about 0.2 mL/100 g alloy melt. 
     
     
         17 . A method as claimed in  claim 14 , wherein the grain refiner of step (v) includes up to about 3.5 wt. % Al 3 Ti 3 B or AlTi 3 B. 
     
     
         18 . A method as claimed in  claim 14 , wherein the grain refiner of step (v) has a B content from about 0.004 to about 0.04 wt. %. 
     
     
         19 . A method as claimed in  claim 14 , wherein in step (vi) the amount of Sr is from about 0.008 to about 0.02 wt. %. 
     
     
         20 . A method as claimed in  claim 14 , wherein the solution heat treatment of step (vii) is carried out at a temperature from about 535° C. to about 540° C. for a time from about 8 h to about 10 h. 
     
     
         21 . A method as claimed in  claim 14 , wherein the ageing heat treatment of step (viii) is carried out at a temperature of about 170° C. from about 7 h to about 8 h. 
     
     
         22 . A method as claimed in  claim 14 , wherein the ageing heat treatment of step (viii) is carried out at a temperature from about 180 to about 190° C. from about 2 h to about 5 h.