Patent ID: 8273196

Claim:
A cold press forming method for an aluminum alloy sheet, comprising: providing an Al—Mg—Si based aluminum alloy sheet blank in an age-precipitated state due to normal-temperature aging; subjecting said aluminum alloy sheet blank to a partial reversion heating treatment; and cold press forming said aluminum alloy sheet blank with a punch while holding down an end part of said aluminum alloy sheet blank, wherein the partial reversion heating treatment comprises the steps of: rapidly heating a heated part of said aluminum alloy sheet blank at a temperature rise rate of not less than 50° C/min to a temperature in the range of 180 to 350° C. so as to momentarily dissolve age-precipitates and soften said heated part, while a non-heated part of said aluminum alloy sheet blank is not heated, whereby the strength of said heated part is lowered as compared with the strength of said non-heated part; holding said sheet blank at a temperature in said range for a time of not more than 5 minutes, including (a time of 0 seconds), and then rapidly cooling said heated part to room temperature at a cooling rate of not less than 50° C/min to a temperature of 100° C. or below, where the heated part is the whole part or a smaller-than-whole part of a portion on the outer side of a region of said aluminum alloy sheet blank to be contacted by a punch shoulder part at the time of press forming, and the non-heated part is the other part than said heated part of said aluminum alloy sheet blank, whereby the difference between the tensile strength of said heated part and the 0.2% proof stress of said non-heated part is increased by not less than 20 MPa through said partial reversion heating treatment; holding said heated part of said rolled sheet between a die and a wrinkle holding down application; and cold press forming said rolled sheet by pushing said non-heated part of said rolled sheet with a punch before the strength of said heated part is returned to the level before said partial reversion heating treatment due to age precipitation during holding at room temperature, so that a limit drawing ratio (LDR) of the cold press forming is higher by at least 0.1 than the LDR in a method without the partial reversion heating treatment.