Substantially Pb-Free Aluminum Alloy Composition

Abstract

A substantially Pb-free aluminum alloy consisting essentially of (in weight percent) Si<0.40; Fe<0.70; Cu 5.0-6.0; Zn<0.30; Bi 0.20-0.80; Sn 0.10-0.50 with the remainder being aluminum and incidental impurities. In one embodiment for applications that are sensitive to cracking from stresses generated during machining, the Bi/Sn ratio (in terms of weight percent) is less than 1.32/1 and producing in a T8 temper. On another embodiment for applications that are not sensitive to cracking from stresses during machining but would benefit from smaller machine chip size and more aggressive material removal rates, the aluminum alloy is produced using a T6 temper. The substantially Pb-free aluminum alloy has mechanical properties that include Ultimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength ≥38.0 KSI/262 MPa, and % Elongation ≥10%.

1 . A method for making a substantially Pb-free aluminum alloy comprising the steps:
 a. producing a billet via direct chill casting an aluminum alloy composition comprising the following components (in weight percent of the aluminum alloy composition):   Pb 0-0.10; Si 0-0.40; Fe 0-0.70; Cu 5.0-6.0; Zn 0-0.30; Bi 0.20-0.80; Sn 0.10-0.50;   with the balance being aluminum save for incidental impurities;   said alloy composition having a ratio by weight of Bi/1Sn of less than 1.32/1;   b. optionally homogenizing the cast billet between 900-1020° F. (482-549° C.);   c. extruding the cast billet into a shape for machine stock;   d. solution heat treating the extrusion from step c. by heating to a soak temperature between 900-1020° F. (482-549° C.);   e. drawing the extrusion from step d.; and   f. artificially aging the product of step e. between 275-375° F. (135-191° C.),   
       wherein said substantially Pb-free aluminum alloy has an Ultimate Tensile Strength ≥45.0 KSI/311 MPa, Yield Strength ≥38.0 KSI/262 MPa, and % Elongation minimum ≥10% and Pb-free aluminum alloy can withstand a 0.015″ (0.38 mm) thick machined wall using a 0.969″ (24.6 mm) diameter twist drill at 1500 RPM and 0.037″ (1.27 mm) per revolution feed rate with <10% failing for wall tearing or cracking. 
     
     
         2 . The method of  claim 1  wherein said aluminum alloy composition comprises the following components (in wt. % of the aluminum alloy composition):
 Si 0-0.16; Fe 0-0.50; Cu 5.1-5.8; Zn 0-0.05; Bi 0.20-0.40; and Sn 0.20-0.50. 
 
     
     
         3 . The method of  claim 1  wherein said aluminum alloy composition has a ratio by weight Bi/Sn in the range from 0.8/1 to 1.32/1. 
     
     
         4 . The method of  claim 1  where the draw reduction is greater than 5% cross sectional area reduction. 
     
     
         5 . The method of  claim 1  where the step of artificially aging is a two-step cycle with a first cycle within the temperature range of 200-300° F. (93-149° C.) and a second step within the temperature range of 275-375° F. (135-191° C.). 
     
     
         6 . The method of  claim 1  wherein said the alloy composition has <0.05 wt. % Pb. 
     
     
         7 . The method of  claim 1  wherein said alloy composition comprises the following components (in wt. % of the aluminum alloy composition):
 <0.05 wt. % Pb, 0.10-0.16 wt. % Si, 0.30-0.50 wt. % Fe, 5.1-5.8 wt. % Cu, 0.002-0.05 wt. % Zn, 0.20-0.80 wt. % Bi, and 0.20-0.50 wt. % Sn. 
 
     
     
         8 . The method of  claim 1  wherein said alloy composition consists of the following components (in wt. % of the aluminum alloy composition):
 <0.05 wt. % Pb, 0.10-0.16 wt. % Si, 0.30-0.50 wt. % Fe, 5.1-5.8 wt. % Cu, 0.002-0.05 wt. % Zn, 0.20-0.80 wt. % Bi, and 0.20-0.50 wt. % Sn with the balance being aluminum and incidental impurities. 
 
     
     
         9 . The method of  claim 1  comprising the steps:
 homogenizing the cast billet between 900-1020° F. (482-549° C.) for a time period of not less than 1 hour; and 
 solution heat treating the extrusion from by heating to a soak temperature between 900-1020° F. (482-549° C.) for 0.5 to 2 hours. 
 
     
     
         10 . A method for making a substantially Pb-free aluminum alloy comprising the steps:
 a. producing a billet via direct chill casting an aluminum alloy composition comprising the following components (in weight percent of the aluminum alloy composition):   Pb 0-0.10; Si 0-0.40; Fe 0-0.70; Cu 5.0-6.0; Zn 0-0.30; Bi 0.20-0.80; Sn 0.10-0.50 with the balance being aluminum save for incidental impurities;   said alloy composition having a ratio by weight of Bi/Sn of less than 1.32/1;   b. optionally homogenizing the cast billet between 900-1020° F. (482-549° C.);   c. extruding the cast billet into a shape for machine stock;   d. optionally drawing the product of step c.;   e. solution heat treating the extrusion between 900-1020° F. (482-549° C.);   f. optionally stretch stress relieving the product of step e.;   g. artificial aging the extruded cast billet between 275-375° F. (135-191° C.), wherein said substantially Pb-free aluminum alloy has an Ultimate Tensile Strength >/=45.0 KSI/311 MPa, Yield Strength >/=38.0 KSI/262 MPa and Elongation >/=10% and the Pb-free aluminum alloy has superior machinability when compared to a product having the same aluminum alloy composition in a T8 temper as determined by chip size (chips per gram) as measured in the following machining operations:
 a) drilling operation at 650 SFPM and 0.075″ (1.91 mm) per revolution feed rate 
 b) cutoff operation at 550 SFPM and 0.0025″ (0.06 mm) per revolution feed rate 
 c) turning operation at 550 SFPM and 0.014″ (0.36 mm) per revolution feed rate 
 d) forming operation at 150 SFPM and 0.003″ (0.076 mm) per revolution feed rate 
 wherein a greater number of chips per gram is considered a superior measure of machinability. 
   
     
     
         11 . The method of  claim 10  wherein said aluminum alloy composition comprises the following components (in wt. % of the aluminum alloy composition):
 Si 0-0.16; Fe 0-0.50; Cu 5.1-5.8; Zn 0-0.05; Bi 0.20-0.40; and Sn 0.20-0.50. 
 
     
     
         12 . The method of  claim 10  wherein said the alloy composition has <0.05 wt. % Pb. 
     
     
         13 . The method of  claim 10  wherein said alloy composition comprises the following components (in wt. % of the aluminum alloy composition):
 <0.05 wt. % Pb, 0.10-0.16 wt. % Si, 0.30-0.50 wt. % Fe, 5.1-5.8 wt. % Cu, 0.002-0.05 wt. % Zn, 0.20-0.80 wt. % Bi, and 0.20-0.50 wt. % Sn. 
 
     
     
         14 . The method of  claim 10  wherein said alloy composition consists of the following components (in wt. % of the aluminum alloy composition):
 <0.05 wt. % Pb, 0.10-0.16 wt. % Si, 0.30-0.50 wt. % Fe, 5.1-5.8 wt. % Cu, 0.002-0.05 wt. % Zn, 0.20-0.80 wt. % Bi, and 0.20-0.50 wt. % Sn with the balance being aluminum and incidental impurities. 
 
     
     
         15 . The method of  claim 10  wherein said aluminum alloy composition has a ratio by weight Bi/Sn in the range from 0.8/1 to 1.32/1. 
     
     
         16 . The method of  claim 10  where the step of artificially aging is a two-step cycle with a first cycle within the temperature range of 200-300° F. (93-149° C.) and a second step within the temperature range of 275-375° F. (135-191° C.).