Al-Mg Alloy Sheet with Excellent Formability at High Temperatures and High Speeds and Method of Production of Same

Abstract

To provide an aluminum alloy sheet with excellent formability at high temperatures and high speeds with a reduced amount of cavities after forming and a method of production of the same. An aluminum alloy sheet consisting of 2.0-8.0 wt % of Mg, 0.06-0.2 wt % of Si, 0.1-0.5 wt % of Fe, 0.1-0.5 wt % of Mn, and the balance of Al and unavoidable impurities, wherein a density of inter-metallic compounds having an equivalent circle diameter of 1 to 5 μm is 5000/mm 2 or more and an average crystal grain size is 20 μm or less. A method of production of an aluminum alloy sheet comprising the steps of casting an alloy melt having the above described composition by a twin belt casting machine at a cooling rate of 20 to 150° C./sec at the location of ¼ of the slab thickness during the casting to form a slab having a thickness of 5 to 15 mm, subsequently rewinding up the slab as a coil, cold rolling the slab taken out from the coil at a cold rolling reduction of 70 to 96%, and performing annealing heating the obtained cold rolled sheet at a heating rate of 50° C./sec or more to 420 to 500° C.

1 . An aluminum alloy sheet with excellent formability at high temperatures and high speeds with a reduced amount of cavities after forming characterized in that it consists of: 
 Mg: 2.0-8.0 wt %,    Si: 0.06-0.2 wt %,    Fe: 0.1-0.5 wt %,    Mn: 0.1-0.5 wt %, and    the balance of Al and unavoidable impurities, wherein    a density of an inter-metallic compound having an equivalent circle diameter of 1 to 5 mm is 5000/mm2 or more and an average crystal grain size is 20 mm or less.    
   
   
       2 . An aluminum alloy sheet as set forth in  claim 1 , characterized by further containing Cu: 0.1 to 0.5 wt %.  
   
   
       3 . An aluminum alloy sheet as set forth in  claim 1 , characterized by further containing at least one of Zr: 0.1 to 0.4 wt % and Cr: 0.1 to 0.4 wt %.  
   
   
       4 . An aluminum alloy sheet as set forth in  claim 1 , characterized in that an elongation during tensile deformation at a strain rate of 0.1 to 1.0/sec in a temperature region of 400 to 550° C. is at least 200%.  
   
   
       5 . An aluminum alloy sheet as set forth in  claim 4 , characterized in that a cavity ratio in a cross-section after breakage due to the tensile deformation is not more than 1%.  
   
   
       6 . A method of production of an aluminum alloy sheet with excellent formability at high temperatures and high speeds with a reduced amount of cavities after forming as set forth in any one of  claim 1 , characterized in that said method comprises the steps of: 
 preparing an alloy melt having a composition as set forth in any one of  claims 1  to  3 ,    casting the alloy melt by a twin belt casting machine at a cooling rate of 20 to 150° C./sec at the location of ¼ of the slab thickness during casting to form a slab having a thickness of 5 to 15 mm,    subsequently rewinding up the slab as a coil,    cold rolling the slab taken out from the coil with a cold rolling reduction of 70 to 96%, and    performing annealing for heating the obtained cold rolled sheet at a heating rate of 5° C./sec or more to 420 to 500° C.