Wednesday, November 30, 2016

Bearing Design Guide: Chapter Nineteen: Heat Treatment of Aluminum Bronze Alloys

C95400 Cast Aluminum Bronze

          The cast aluminum bronzes consist of copper and aluminum with lesser additions of iron, nickel or manganese elements, primarily to enhance the tensile strength, yield strength, hardness, wear resistance, fatigue resistance and corrosion.
          The more popular aluminum bronzes contain from 8 to 13 % aluminum, up to 5% iron, nickel and manganese in various combinations.

          As the aluminum content increases, the tensile strength, yield strength and hardness also increase but ductility decreases.

          The aluminum bronze alloys with 10% or more aluminum content can be heat-treated successfully to further increase the physical and mechanical properties of the alloy.

         The normal heat treatment sequence of aluminum bronze alloys with 10% or more aluminum content is to solution heat soak the alloy at 1650 degrees F for at least two hours, then quenching rapidly in water. Slow cooling results in "self-annealing" and produces a coarse structure with greatly-reduced properties.

          Following the heat-treatment sequence, a tempering treatment is required by reheating the casting to 1000 to 1150 degrees F for one hour then quenching in water.

          The heat-treatment changes the "as cast" alloy's micro-structure to a finer grain, resulting in substantial increases in tensile strength, yield strength and hardness but with a fairly high reduction in ductility.

          The wear resistance also is greatly improved by heat treatment without correlation to hardness. It does not seem to cause increased damage to steel shafts.

Solution Heat Treating
That's it for today.  Until next time my metal loving friends...

Next Up: Chapter 20: Thrust Bearings or Washers

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