System and method for heat treating aluminum alloy castings

Abstract

A method for heat treating cast aluminum alloy components that includes obtaining a casting formed from an aluminum alloy having a silicon constituent and at least one metal alloying constituent, and heating the casting to a first casting temperature that is below but within 10° C. of a predetermined silicon solution temperature at which the silicon constituent rapidly enters into solid solution. The method also includes increasing the rate of heat input into the casting to raise the temperature of the casting to a second casting temperature that is above but within 10° C. of a predetermined alloying metal solution temperature at which the at least one metal alloying constituent rapidly enters into solid solution, maintaining the casting at the second casting temperature for a period of time that is less than about 20 minutes, and then quenching the casting to a temperature less than or about 250° C.

What is claimed is: 
     
         1 . A method for heat treating a casting formed from an aluminum alloy having a silicon constituent and at least one metal alloying constituent, the method comprising:
 heating the casting to a first casting temperature less than 10° C. below a predetermined silicon solution temperature at which the silicon constituent rapidly enters into solid solution;   increasing the rate of heat input into the casting to heat the casting to a second casting temperature less than 10° C. above a predetermined alloying metal solution temperature at which the at least one metal alloying constituent rapidly enters into solid solution;   maintaining the casting at the second casting temperature for a period of time less than about 20 minutes; and   quenching the casting to a temperature less than about 250° C.   
     
     
         2 . The method of  claim 1 , wherein the first casting temperature is less than 5° C. below the predetermined silicon solution temperature. 
     
     
         3 . The method of  claim 1 , wherein the second casting temperature is less than 5° C. above the predetermined alloying metal solution temperature. 
     
     
         4 . The method of  claim 1 , wherein the casting has been formed in a high pressure die cast process. 
     
     
         5 . The method of  claim 1 , further comprising maintaining the casting at the first casting temperature for a period of time greater than about 2 minutes prior to increasing the rate of heat input into the casting. 
     
     
         6 . The method of  claim 1 , further comprising maintaining the casting at the second casting temperature for a period of time greater than about 2 minutes. 
     
     
         7 . The method of  claim 1 , further comprising maintaining the casting at the second casting temperature until the casting achieves a time-in-treatment ratio greater than about 50%, the time-in-treatment ratio being defined by a duration of time the casting spent above the predetermined alloying metal solution temperature divided by a duration of time the casting spent above the predetermined silicon solution temperature. 
     
     
         8 . The method of  claim 7 , wherein the casting achieves a time-in-treatment ratio between about 70% and about 90%. 
     
     
         9 . The method of  claim 1 , further comprising heating the casting from the first casting temperature to within 5° C. of the second casting temperature in a period of time that is less than about 5 minutes. 
     
     
         10 . The method of  claim 1 , wherein the silicon constituent comprises between about 6 weight percent and about 20 weight percent of the aluminum alloy. 
     
     
         11 . The method of  claim 1 , wherein the at least one metal alloying constituent is selected from the group consisting of copper, magnesium, and manganese. 
     
     
         12 . A method for heat treating die cast aluminum alloy casting having a silicon constituent and at least one metal alloying constituent, the method comprising:
 moving a casting into a first heating stage of a furnace maintained at a first stage temperature;   heating the casting to a first casting temperature less than 10° C. below a predetermined silicon solution temperature at which the silicon constituent rapidly enters into solid solution;   moving the casting from the first heating stage into a second heating stage of the furnace that is separate from the first heating stage and maintained at a second stage temperature that is greater than the first stage temperature;   increasing the rate of heat input into the casting to heat the casting to a second casting temperature less than 10° C. above to a predetermined alloying metal solution temperature at which the at least one metal alloying constituent rapidly enters into solid solution;   maintaining the casting at the second casting temperature for a period of time less than about 20 minutes;   removing the casting from the second heating stage of the furnace; and   quenching the casting to a temperature less than about 250° C.   
     
     
         13 . The method of  claim 12 , further comprising maintaining the casting at the second casting temperature until the casting achieves a time-in-treatment ratio greater than about 50%, the time-in-treatment ratio being defined by a duration of time the casting spent above the predetermined alloying metal solution temperature divided by a duration of time the casting spent above the predetermined silicon solution temperature. 
     
     
         14 . The method of  claim 13 , wherein the casting achieves a time-in-treatment ratio between about 70% and about 90%. 
     
     
         15 . The method of  claim 12 , further comprising heating the casting from the first casting temperature to within 5° C. of the second casting temperature in a period of time that is less than about 5 minutes. 
     
     
         16 . The method of  claim 12 , wherein moving the casting from the first heating stage into the second heating stage further comprises moving the casting through an intermediate door separating the first heating stage and the second heating stage. 
     
     
         17 . A system for heat treating an aluminum alloy casting having a silicon constituent and at least one metal alloying constituent, the system comprising:
 a first heating stage configured to heat the casting to a first casting temperature that is less than 10° C. below a predetermined silicon solution temperature at which the silicon constituent rapidly enters into solid solution;   a second heating stage configured to increase the rate of heat input into the casting to heat the casting to a second casting temperature that is less than 10° C. above a predetermined alloying metal solution temperature at which the at least one metal alloying constituent rapidly enters into solid solution;   an intake door defining the beginning of the first heating stage;   an intermediate door separating the first heating stage and the second heating stage;   a discharge door defining the end of the second heating stage; and   at least one transport apparatus configured to convey the casting from the intake door through the first heating stage and the second heating stage to the discharge door.   
     
     
         18 . The system of  claim 17 , wherein the at least one transport apparatus is configured to maintain the plurality of castings within the second heating stage for a period of time greater than about 3 minutes and less than about 30 minutes. 
     
     
         19 . The system of  claim 17 , wherein the at least one transport apparatus is configured convey the plurality of castings through the furnace from the intake door through to the discharge door at a substantially constant speed. 
     
     
         20 . The method of  claim 19 , wherein the at least one transport apparatus further comprises a conveyor chain. 
     
     
         21 . The method of  claim 20 , wherein the location of the intermediate door is repositionable along a length of the furnace. 
     
     
         22 . The system of  claim 17 , wherein the at least one transport apparatus is configured convey the plurality castings through the first heating stage of the furnace at a first speed and through the second heating stage of the furnace at a second speed that is different from the first speed. 
     
     
         23 . The system of  claim 22 , wherein the at least one transport apparatus further comprises at least two conveyor chains. 
     
     
         24 . The system of  claim 17 , further comprising at least one high flow hot air nozzle downstream and adjacent to the intermediate door for directing heated air onto the plurality of castings upon entrance into the second heating stage. 
     
     
         25 . A method for heat treating a casting formed from an aluminum alloy having a silicon constituent and at least one metal alloying constituent, the method comprising:
 heating the casting to a first casting temperature less than a predetermined silicon solution temperature at which the silicon constituent rapidly enters into solid solution;   heating the casting to a second casting temperature greater than a predetermined alloying metal solution temperature at which the at least one metal alloying constituent rapidly enters into solid solution;   maintaining the casting at the second casting temperature for a period of time greater than about 5 minutes and less than about 20 minutes; and   quenching the casting to a temperature less than about 250° C.   
     
     
         26 . The method of  claim 25 , further comprising maintaining the casting at the second casting temperature until the casting achieves a time-in-treatment ratio greater than about 50%, the time-in-treatment ratio being defined by a duration of time the casting spent above the predetermined alloying metal solution temperature divided by a duration of time the casting spent above the predetermined silicon solution temperature.