Combination of casting process and alloy compositions resulting in cast parts with superior combination of elevated temperature creep properties, ductility and corrosion performance

Abstract

A process for casting a magnesium alloy consisting of 2.0-6.00% by weight of aluminium, 3.00-8.00% by weight of rare earth metals (RE-metals), the ratio of the amount of RE-metals to the amount of aluminium expressed as % by weight being larger than 0.8, at least 40% by weight of the RE-metals being cerium, less than 0.5% by weight of manganese, less than 1.00% by weight of zinc, less than 0.01% by weight of calcium less than 0.01% by weight of strontium and the balance being magnesium and unavoidable impurities, the total impurity level being below 0.1% by weight, wherein the alloy is cast in a die the temperature of which is controlled in the range of 180-340° C., the die is filled in a time which expressed in milliseconds is equal to the product of a number between 5 and 500 multiplied by the average part thickness expressed in millimeter, the static metal pressures being maintained during casting between 20-70 MPa and is subsequently intensified up to 180 MPa.

1 : A process for casting a magnesium alloy consisting of
 2.0-6.00% by weight of aluminum,   3.00-8.00% by weight of rare earth metals,   the ratio of the amount of rare earth metals to the amount of aluminum expressed as a percentage by weight being larger than 0.8,   at least 40% by weight of the rare earth metals being cerium,   less than 0.5% by weight of manganese,   less than 1.00% by weight of zinc,   less than 0.01% by weight of calcium,   less than 0.01% by weight of strontium,   and the balance being magnesium and unavoidable impurities, the total impurity level being below 0.1% by weight, the process comprising:
 casting the alloy in a die, the temperature of which is controlled in the range of 180-340° C., 
 filing the die in a time which expressed in milliseconds is equal to the product of a number between 5 and 500 multiplied by the average part thickness expressed in millimeters, and 
   maintaining static metal pressures during casting between 20-70 MPa, with subsequent intensification up to 180 MPa.   
   
   
       2 : The process according to  claim 1 , wherein the die temperature is controlled to a temperature in the range between 200 and 270° C. 
   
   
       3 : The process according to  claim 1 , wherein the filling time of the die expressed in milliseconds is equal to product of the average part thickness expressed in millimeters multiplied by a number between 5 and 20. 
   
   
       4 : The process according to  claim 1 , wherein the static metal pressure during casting is maintained between 30-70 MPa. 
   
   
       5 : The process according to  claim 1 , wherein a cooling rate after casting is in the range of 10-1000° C./s. 
   
   
       6 : The process according to  claim 1 , wherein the aluminum content is between 2.50 and 5.50% by weight. 
   
   
       7 : The process according to  claim 1 , wherein the rare earth metal content is between 3.50 and 7.00% by weight. 
   
   
       8 : The process according to  claim 1 , wherein the aluminum content is between 3.6 and 4.5% by weight and the rare earth metal content is between 3.6 and 4.5% by weight, and ratio of the amount of rare earth metals to the amount of aluminum is larger than 0.9. 
   
   
       9 : The process according to  claim 1 , wherein the aluminum content is between 2.6 and 3.5% by weight and the rare earth metal content is greater than 4.6% by weight. 
   
   
       10 : The process according to  claim 1 , wherein the rare earth metals are selected from the group consisting of cerium, lanthanum, neodymium and praseodymium. 
   
   
       11 : The process according to  claim 10 , wherein the amount of lanthanum is at least 15% by weight of the total content of rare earth metals. 
   
   
       12 : The process according to  claim 10 , wherein the amount of lanthanum is at most 35% by weight of the total content of rare earth metals. 
   
   
       13 : The process according to  claim 10 , wherein the amount of neodymium is at least 7% by weight of the total content of rare earth metals. 
   
   
       14 : The process according to  claim 10 , wherein the amount of neodymium is at most 20% by weight of the total content of rare earth metals. 
   
   
       15 : The process according to  claim 10 , wherein the amount of praseodymium is at least 2% by weight of the total content of rare earth metals. 
   
   
       16 : The process according to  claim 10 , wherein the amount of praseodymium is at most 10% by weight of the total content of rare earth metals. 
   
   
       17 : The process according to  claim 10 , wherein the amount of cerium is greater than 50% by weight of the total content of rare earth metals. 
   
   
       18 : The process according to  claim 10 , wherein the amount of calcium and/or strontium is a maximum of 0.01% by weight.