Aluminium based casting alloy

Abstract

An aluminium based alloy has a weight percentage composition of from 5 to 15% silicon, 0 to 0.25% magnesium, 0 to 0.25% titanium, 0.2 to 0.65% manganese, 0.1 to 0.6% iron, 1 to 4% copper, 0 to 3% zinc, less than 0.01% in total of silicon modifiers (with less than 0.007% strontium), less than 0.05% tin, less than 0.2% in total of other transition or rare earth metals (with less than 0.05% chromium), less than 0.5% in total other elements, and a balance of aluminium. The limits for iron and manganese are constrained such that the amount of iron present in the alloy is 0.4 to 1.6 times the manganese content and the alloy has a sludge factor (SF), calculated as SF=(1×wt % Fe)+(2×wt % Mn), of from 0.8 to 1.6. A casting made from the alloy has enhanced fracture resistance relative to casting of the same product made of a conventional HPDC alloy when compared in the as cast or same heat treated state.

1 . An aluminium based alloy according to the invention has a weight percentage composition of: 
       
         
           
                 
                 
               
                     
                 
                   silicon 
                    5 to 15% 
                 
                   magnesium 
                     0 to 0.25% 
                 
                   titanium 
                     0 to 0.25% 
                 
                   manganese 
                    0.2 to 0.65% 
                 
                   iron 
                   0.1 to 0.6% 
                 
                   copper 
                   1 to 4% 
                 
                   zinc 
                   0 to 3% 
                 
                   silicon modifiers 
                   less than 0.01% in total 
                 
                     
                   (with less than 0.007% strontium) 
                 
                   tin 
                   less than 0.05% 
                 
                   other transition or rare earth metals 
                   less than 0.2% in total 
                 
                     
                   (with less than 0.05% chromium) 
                 
                   other elements 
                   less than 0.5% in total, 
                 
                     
                 
                   and a balance of aluminium, 
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         wherein the limits for iron and manganese are constrained such that the amount of iron present in the alloy is 0.4 to 1.6 times the manganese content and the alloy has a sludge factor (SF), calculated as SF=(1×wt % Fe)+(2×wt % Mn), of from 0.8 to 1.6. 
       
     
     
         2 . The alloy of  claim 1 , wherein the chromium level is less than 0.02% 
     
     
         3 . The alloy of  claim 1  or  claim 2 , wherein the composition is free of beryllium, rare earth elements, and free of chromium and other transition metal elements not including Ti, Mn, Fe, Cu and Zn. 
     
     
         4 . The alloy of any one of  claims 1  to  3 , wherein the silicon level is from 6.5 to 10.5% such as from 6.5 to 8.5%. 
     
     
         5 . The alloy of any one of  claims 1  to  4 , wherein copper is present at from 1 to 3.5% such as from 1.5 to 3%. 
     
     
         6 . The alloy of any one of  claims 1  to  5 , wherein SF=1.0 to 1.3. 
     
     
         7 . The alloy of any one of  claims 1  to  6 , wherein the iron content is from 0.5 to 0.9 times the manganese content by weight. 
     
     
         8 . The alloy of any one of  claims 1  to  7 , wherein the iron content is from 0.2 to 0.4% and the Mn content is from 0.3 to 0.6%. 
     
     
         9 . The alloy of any one of  claims 1  to  8 , wherein zinc is present at from 0.3 to 1.0%. 
     
     
         10 . The alloy of any one of  claims 1  to  9 , wherein magnesium is present at from 0.05 to 0.15%. 
     
     
         11 . A casting having enhanced fracture resistance relative to casting of the same product made of a conventional HPDC alloy when compared in the as cast or same heat treated state, wherein the casting having enhanced fracture resistance is cast from an aluminium based alloy having a weight percentage composition of: 
       
         
           
                 
                 
               
                     
                 
                   silicon 
                    5 to 15% 
                 
                   magnesium 
                     0 to 0.25% 
                 
                   titanium 
                     0 to 0.25% 
                 
                   manganese 
                    0.2 to 0.65% 
                 
                   iron 
                   0.1 to 0.6% 
                 
                   copper 
                   1 to 4% 
                 
                   zinc 
                   0 to 3% 
                 
                   silicon modifiers 
                   less than 0.01% in total 
                 
                     
                   (with less than 0.007% strontium) 
                 
                   tin 
                   less than 0.05% 
                 
                   other transition or rare earth metals 
                   less than 0.2% in total 
                 
                     
                   (with less than 0.05% chromium) 
                 
                   other elements 
                   less than 0.5% in total, 
                 
                     
                 
                   and a balance of aluminium, 
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         wherein the limits for iron and manganese are constrained such that the amount of iron present in the alloy is 0.4 to 1.6 times the manganese content and the alloy has a sludge factor (SF), calculated as SF=(1×wt % Fe)+(2×wt % Mn), of from 0.8 to 1.6; and 
         wherein the casting having enhanced fracture toughness has a microstructure exhibiting silicon formed from solidified eutectic which also contains iron-bearing phases which are substantially fine polyhedral particles. 
       
     
     
         12 . The casting having enhanced fracture resistance according to  claim 11 , wherein the casting is cast from the alloy of any one of  claims 2  to  10 . 
     
     
         13 . The casting having enhanced fracture resistance according to  claim 11 , wherein the casting is in the as cast condition. 
     
     
         14 . The casting having enhanced fracture resistance according to  claim 11 , wherein the casting has its fracture resistance and/or microstructure enhanced relative to the as cast condition by heat treatment.