Method for producing Al-Mg-Si alloy sheet excellent in bake-hardenability and hemmability

Abstract

[PROBLEMS] To provide a method for producing an aluminum alloy sheet excellent in bake-hardenability and hemmability at a low cost by the employment of a very short production process. [MEANS FOR SOLVING PROBLEMS] A method for producing an aluminum alloy sheet, which comprises providing an aluminum alloy melt having a chemical composition, in wt %, that Mg: 0.30 to 1.00%, Si: 0.30 to 1.20%, Fe: 0.05 to 0.50%, Mn: 0.05 to 0.50%, Ti: 0.005 to 0.10%, optionally further one or more of Cu: 0.05 to 0.70% and Zr: 0.05 to 0.40%, and the balance: Al and inevitable impurities, casting the alloy melt into a slab having a thickness of 5 to 15 mm by the twin belt casting method with a cooling speed at ¼ of the thickness of the slab of 40 to 150° C./s, winding up a coil, subjecting the coil to a homogenizing treatment, cooling the resultant coil to a temperature of 250° C. or lower with a cooling speed of 500° C./hr or more, followed by cold rolling, and then subjecting the resulting product to a solution treatment.

1 . A method of producing aluminum alloy sheets excelling in bake-hardenability and hemmability, comprising steps of casting, by means of a twin-belt casting method, an alloy melt comprising 0.30-1.00 wt % of Mg, 0.30-1.20 wt % of Si, 0.05-0.50 wt % of Fe, 0.05-0.50 wt % of Mn and 0.005-0.10 wt % of Ti, optionally further comprising at least one of 0.05-0.70 wt % of Cu or 0.05-0.40 wt % of Zr, the remainder consisting of Al and unavoidable impurities, to form a 5-15 mm thick slab at a cooling rate of 40-150° C./s at a quarter-thickness of the slab; winding into a coil; subjecting to a homogenization treatment by inserting the coil into a batch furnace, heating to 520-580° C. at a heating rate of at least 30° C./h, then holding at that temperature for 2-24 hours; cooling to 250° C. or less at a cooling rate of at least 500° C./h; cold rolling; then subjecting to a solution treatment by heating to 530-560° C. at a heating rate of at least 10° C./s in a continuous annealing line, and holding for 30 seconds or less.  
   
   
       2 . (canceled)  
   
   
       3 . (canceled)  
   
   
       4 . A method in accordance with  claim 1 , comprising steps, after said solution treatment, of cooling to room temperature at a cooling rate of at least 10° C./s, then subjecting to a restoration treatment by holding for 30 seconds or less at 260-300° C. in a continuous annealing furnace, and cooling to room temperature at a cooling rate of at least 10° C./s.  
   
   
       5 . A method in accordance with  claim 1 , comprising steps, after said solution treatment, of water-cooling to 250° C. or less at a cooling rate of at least 10° C./s, then air-cooling to 60-100° C. at a cooling rate of 1-20° C./s, coiling up, and subjecting to a preliminary ageing treatment by cooling to room temperature.  
   
   
       6 . A method in accordance with  claim 1 , comprising steps, after said solution treatment, of cooling to room temperature at a cooling rate of at least 10° C./s, then subjecting to a restoration treatment by holding for 30 seconds or less at 260-300° C. in a continuous annealing furnace, cooling to 60-100° C. at a cooling rate of at least 1° C./s, coiling up, and subjecting a preliminary ageing treatment by cooling to room temperature.  
   
   
       7 . A method in accordance with  claim 1  further comprising the step of, after said homogenization treatment, removing the coil from the batch furnace and forcibly cooling while unwinding the coil.