Selecting A Casting Alloy

Common Castings Considerations
  • Greater Flexibility In Designing Complex Shapes.
  • Dissipate Stress That Cause Fatigue Cracking.
  • Blending Shapes That Adhere To Clearance Issues.
  • Move Fabrication / Weld Joints To Low- Stress Areas Or Eliminate Fab Joints!
  • Provide Durability Resistance To Impact Loads.
  • Weight Enhancement

Most of the common alloys can be cast using expendable molds of some kind. But their use in reusable mold depends on their melting points. A reusable mold process can't be used if the melting point of the alloy is higher.

Each alloy has its own strengths and weaknesses with regard to cost, reliability, dimensions held, metallurgical quality, volume production and competitive situation. Things to be considered, while selecting an alloy, are as follows:

  • Cost
  • Strength
  • Hot strength
  • Hardness
  • Density (weight limitations)
  • Bearing qualities (galling resistance)
  • Machinability
  • Weldability
  • Brazability
  • Brazability
  • Abrasion resistance
  • Corrosion resistance
  • Oxidation resistance
  • Fatigue properties
  • Resistance to crack propagation
  • Electrical conductivity
  • Magnetic properties
  • Thermal conductivity

Followings are the two tables that may be useful in Selecting a Casting Alloy :

Followings are the two tables that may be useful in Selecting a Casting Alloy :

Alloy Fitness for Reusable Mold Processes
(Ordered lowest to highest by melting point)
Base Maximum Strength (1000s psi) Reusable Mold
Zinc 61 Yes
Aluminum 60 Some alloys
Magnesium 40 Yes
Copper 150 Some alloys
Cast iron 60 Some alloys
Cobalt 110 No
Nickel 130 No
Stainless steel 200 No
Tool steel 220 No
Maraging steel 240 No
Low alloy steel 220 No
Carbon steel 150 No
Titanium 160 No

Comparison Chart For Various Alloys
Aluminum Alloys
  • Second most plentiful metal on earth
  • Hall-Heroult process electrolytic reductionof Al2O3 to liquid metal
  • One-third the density of Steel
  • Aluminum alloys can be up to 30 times stronger than pure Aluminum
  • Wrought & Casting Alloys
  • Al Li Alloys
Magnesium Alloys
  • Extracted electrolytically from concentrated
  • magnesium chloride in seawater
  • Density = 1.74g/cm3 (lighter then Al)
  • Specific strength comparable to Al
  • Poor corrosion resistance in a marine environment
Beryllium Alloys
  • Modulus of Elasticity = 42 x 106 psi (stiffer then steel)
  • Density = 1.848 g/cm3 (light then Al)
  • Expensive , complicated production
  • It can be toxic, BeO is a carcinogenic material for some people.
Copper Alloys
  • Heavier then Steel, lower specific strength then Aluminum
  • Many copper alloys are excellent electrical conductors
  • Brass - Copper-Zinc alloys w/ < 40% Zn
  • Bronze - Copper-Tin alloys w/ < 10% Sn
  • Copper-Beryllium alloys are non-sparking
Nickel Alloys
  • High temperature alloys
  • Great corrosion resistance
  • Supperalloys - Nickel, iron-nickel, and cobalt. (high strength at high temperatures)
  • Solid solution, dispersion strengthening and precipitation hardening
Titanium Alloys
  • The Kroll process - conversion of TiO2 to TiCl4 which is then reduced to titanium metal
  • Higher specific strength then aluminum
  • Excellent corrosion resistance and high temperature properties
  • Alpha (a) and Beta (b) titanium alloys
Refractory Metals
  • Exceptionally high melting temperatures
  • Tungsten (W) – 3,410oC
  • Molybdenum (Mo) – 2,610oC
  • Tantalum (Ta) – 2,996oC
  • Niobium or Columbium (Nb) - 2,468oC
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