Cast aluminum alloy excellent in relaxation resistance property and method of heat-treating the same

Abstract

A cast aluminum alloy excellent in the relaxation resistance property, comprising 9 to 17% by mass of Si, 3 to 6% by mass of Cu, 0.2 to 1.2% by mass of Mg, 0.2 to 1.5% by mass of Fe, 0.1 to 1% by mass of Mn, a balance consists of Al and unavoidable impurities, wherein a Ni content is not more than 0.5% by mass. The average hardness is adjusted to HV130 to HV160 by performing, after casting, solution heating by retaining the alloy at a treatment temperature of 450 to 510° C. for 0.5 hour or longer, performing water quenching and, thereafter, performing aging treatment by retaining the alloy at a treatment temperature of 170 to 230° C. for 1 to 24 hours.

1 . A cast aluminum alloy excellent in the relaxation resistance property, comprising:
 9 to 17% by mass of Si,   3 to 6% by mass of Cu,   0.2 to 1.2% by mass of Mg,   0.2 to 1.5% by mass of Fe,   0.1 to 1% by mass of Mn, and   a balance consisting of Al and unavoidable impurities,
 wherein a content of Ni is not more than 0.5% by mass, and 
 an average hardness is HV130 to HV160. 
   
     
     
         2 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 1 , wherein the average hardness is adjusted by performing, after casting, solution heating by retaining the alloy at a treatment temperature of 450 to 510° C. for 0.5 hour or longer, performing water quenching and, thereafter, performing aging treatment by retaining the alloy at a treatment temperature of 170 to 230° C. for 1 to 24 hours. 
     
     
         3 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 1  or  2 , wherein the alloy has a hypoeutectic structure in which a Si content is 9 to 12% by mass and primary crystal Si is not present. 
     
     
         4 . A cast aluminum alloy excellent in the relaxation resistance property, comprising:
 9 to 17% by mass of Si,   3 to 6% by mass of Cu,   0.3 to 1.2% by mass of Mg,   0.2 to 1% by mass of Fe,   0.1 to 1% by mass of Mn,   0.15 to 0.3% by mass of Ti, and   a balance consisting of Al and unavoidable impurities,
 wherein a content of Ni is not more than 0.5% by mass, and 
 the alloy has an isotropic homogeneous structure in which a ratio of area of dendrite where 5 or more dendrite cells are aligned generally in one direction is not more than 20% in terms of an area ratio, and there is substantially no alignment of dendrites. 
   
     
     
         5 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 4 , further comprising 0.05 to 0.15% by mass of Zr, and 0.02 to 0.15% by mass of V. 
     
     
         6 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 4  or  5 , wherein the alloy has a hypoeutectic structure in which a Si content is 9 to 12% by mass, a P content is not more than 0.001% by mass, and primary crystal Si is not present. 
     
     
         7 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 6 , further comprising at least one member selected from the group consisting of:
 0.0005 to 0.01% by mass of Ca,   0.0005 to 0.003% by mass of Na,   0.003 to 0.03% by mass of Sr, and   0.05 to 0.2% by mass of Sb.   
     
     
         8 . The cast aluminum alloy excellent in the relaxation resistance property according to any one of  claims 4  to  7 , wherein an average hardness is HV130 to HV160. 
     
     
         9 . The cast aluminum alloy excellent in the relaxation resistance property according to  claim 8 , wherein the average hardness is adjusted by performing, after casting, solution heating by retaining the alloy at a treatment temperature of 450 to 510° C. for 0.5 hour or longer, performing water quenching and, thereafter, performing aging treatment by retaining the alloy at a treatment temperature of 170 to 230° C. for 1 to 24 hours. 
     
     
         10 . The cast aluminum alloy excellent in the relaxation resistance property according to any one of  claims 6  to  9 , wherein an average longitudinal diameter of crystallized Si is not more than 5 μm. 
     
     
         11 . The cast aluminum alloy excellent in the relaxation resistance property according to any one of  claims 1  to  10 , further comprising at least one member selected from the group consisting of:
 0.01 to 0.1% by mass of Sn,   0.02 to 0.15% by mass of Pb, and   0.1 to 1% by mass of Zn.   
     
     
         12 . The cast aluminum alloy excellent in the relaxation resistance property according to any one of  claims 1  to  11 , wherein a Si amount in a base Al phase is not less than 0.95% by mass. 
     
     
         13 . A method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property, containing:
 9 to 17% by mass of Si,   3 to 6% by mass of Cu.   0.2 to 1.2% by mass of Mg,   0.2 to 1.5% by mass of Fe,   0.1 to 1% by mass of Mn, and   a balance consists of Al and unavoidable impurities,
 wherein a content of Ni is not more than 0.5% by mass, and 
   the method comprising:   performing, after casting, solution heating by retaining the alloy at a treatment temperature of 450 to 510° C. for 0.5 hour or longer,   performing water quenching and, thereafter,   performing aging treatment by retaining the alloy at a treatment temperature of 170 to 230° C. for 1 to 24 hours,   thereby, adjusting an average hardness at HV130 to HV160.   
     
     
         14 . A method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property, containing:
 9 to 17% by mass of Si,   3 to 6% by mass of Cu.   0.3 to 1.2% by mass of Mg,   0.2 to 1% by mass of Fe,   0.1 to 1% by mass of Mn,   0.15 to 0.3% by mass of Ti, and   a balance consists of Al and unavoidable impurities,
 wherein a content of Ni is not more than 0.5% by mass, and 
   the method comprising:   performing, after casting, solution heating by retaining the alloy at a treatment temperature of 450 to 510° C. for 0.5 hour or longer,
 performing water quenching and, thereafter, 
 performing aging treatment by retaining the alloy at a treatment temperature of 170 to 230° C. for 1 to 24 hours, thereby, adjusting an average hardness at HV130 to HV160. 
   
     
     
         15 . The method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property according to  claim 14 , wherein the cast aluminum alloy further comprises:
 0.05 to 0.15% by mass of Zr, and   0.02 to 0.15% by mass of V.   
     
     
         16 . The method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property according to  claim 14  or  15 , wherein the cast aluminum alloy has a hypoeutectic structure in which a Si content is 9 to 12% by mass, a P content is not more than 0.001% by mass, and primary crystal Si is not present. 
     
     
         17 . The method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property according to  claim 16 , wherein the cast aluminum alloy further contains at least one member selected from the group consisting of:
 0.0005 to 0.01% by mass of Ca,   0.0005 to 0.003% by mass of Na,   0.003 to 0.03% by mass of Sr, and   0.05 to 0.2% by mass of Sb.   
     
     
         18 . The method of heat-treating a cast aluminum alloy excellent in the relaxation resistance property according to any one of  claims 13  to  16 , wherein the cast aluminum alloy further contains at least one member selected from the group consisting of:
 0.01 to 0.1% by mass of Sn,   0.02 to 0.15% by mass of Pb, and   0.1 to 1% by mass of Zn.