Effects of alloying elements on properties of aluminum alloys

Dr. Dmitri Kopeliovich

Alloying elements when added to Aluminum alloys may produce effects of precipitation hardening (age hardening), solid solution hardening, dispersion strengthening, grain refining, modifying metallic and intermetallic phases, suppression of grain growth at elevated temperatures (e.g. during annealing), wear resistance and other tribological properties.

• Silicon, Si (up to 17%)
  • Improves castability of aluminum alloys due to a better fluidity and lower shrinkage of molten aluminum-silicon alloys.
  • Increases strength of the alloys.
  • Improves resistance to abrasive wear.
  • Silicon in a combination with magnesium allows to strengthen the alloys by precipitation hardening heat treatment (Wrought aluminum-magnesium-silicon alloys (6xxx), Cast aluminum alloy 356.0).
• Copper, Cu (up to 6.5%)
  • Increases tensile strength, fatigue strength and hardness of the alloys due to the effect of solid solution hardening.
  • Allows to strengthen the alloys by precipitation hardening heat treatment (Wrought aluminum-copper alloys (2xxx), Cast aluminum alloy 201.0).
  • Decreases the ductility of the alloys.
  • Decreases corrosion resistance.
• Magnesium, Mg (up to 10%)
  • Strengthens and hardens the alloys by solid solution hardening mechanism without considerable decrease of ductility (Wrought aluminum-magnesium alloys (5xxx), Cast aluminum alloy 518.0.
  • In a combination with silicon or zinc allows to strengthen the alloys by precipitation hardening heat treatment (Wrought aluminum-magnesium-silicon alloys (6xxx), Wrought aluminum-zinc-magnesium alloys (7xxx), Cast aluminum alloy 356.0, Cast aluminum alloy 713.0).
• Manganese, Mn (up to 1.5%)
  • Strengthens and hardens the alloys (Wrought aluminum-manganese alloys (3xxx)) by solid solution hardening and dispersion hardening mechanisms.
  • Improves low cycle fatigue resistance.
  • Increases corrosion resistance.
  • Improves ductility of aluminum alloys containing iron and silicon due to modification of Al₅FeSi intermetallic inclusions from platelet to cubic form Al₁₅(MnFe)₃Si₂.
• Zinc, Zn (up to 8%)
  • In a combination with magnesium or magnesium-copper allows to strengthen the alloys by precipitation hardening heat treatment (Wrought aluminum-zinc-magnesium alloys (7xxx), Cast aluminum alloy 713.0).
  • Increases susceptibility of the alloys to Stress corrosion cracking.
• Chromium, Cr (up to 0.3%)
  • Suppresses the grain growth at elevated temperatures (e.g. during heat treatment).
  • Improves ductility and toughness of aluminum alloys containing iron and silicon due to modification of Al₅FeSi intermetallic inclusions from platelet to cubic form (similar to the effect of manganese).
  • Reduces susceptibility of the alloys to Stress corrosion cracking.
• Nickel, Ni (up to 2%)
  • Increases hardness and strength of aluminum-copper (Wrought aluminum-copper alloys (2xxx) and aluminum-silicon (Wrought aluminum-silicon alloy 4032) at elevated temperatures.
  • Reduces the Coefficient of Thermal Expansion.
• Lithium, Li (up to 2.6%)
  • Increases strength by the precipitation hardening heat treatment.
  • Increases Modulus of Elasticity.
  • Reduces density.
• Titanium, Ti (up to 0.35%)
  • Refines primary aluminum grains (grains formed during the Solidification) due to formation of fine nuclei Al₃Ti. Titanium is commonly added to aluminum alloys together with boron due to their synergistic grain refining effect.
• Boron, B (up to 0.03%)
  • Boron in a combination with titanium refines primary aluminum grains (grains formed during the Solidification) due to formation of fine nuclei TiB₂.
• Zirconium, Zr (up to 0.3%); Vanadium, V (up to 0.2%)
  • Inhibit recovery and recrystallization
  • Increase the recrystallization temperature.
• Iron, Fe (up to 1.1%)
  • Increases strength due to formation of Al-Fe intermetallics.
  • Decreases ductility. I most aluminum alloys Iron is undesirable impurity.
• Sodium, Na (up to 0.015%); Antimony, Sb (up to 0.5%); Calcium, Ca (up to 0.015%), Strontium, Sr (up to 0.05%)
  • Increase ductility of hypoeutectic and eutectic aluminum-silicon alloys (Wrought aluminum-silicon alloys (4xxx), Cast aluminum alloy 443.0) by a modification of the silicon phase from coarse platelet like particles to fine fibrous structure.
• Tin, Sn (up to 40%)
  • Reduces coefficient of friction of aluminum alloys (Aluminum based bearing materials).
  • Increases compatibility of the aluminum bearing alloy.
  • Improves conformability.
  • Improves embedability.

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• Classification of aluminum alloys
• Temper designation of aluminum alloys
• Wrought aluminum alloys
• Cast aluminum alloys
• Sintered aluminum alloys
• Fluxes for melting aluminum
• Degassing treatment of molten aluminum alloys
• Aluminum extrusion

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