Aluminum-zinc alloys are used for their strength and corrosion resistance. The zinc in the alloy acts as a buffer and prevents the aluminum from reacting with corrosive substances such as sulfuric acid. The alloy is also relatively inexpensive and easy to work with.
The aluminum-zinc alloy formula is primarily determined by the composition of the molten metal and the method of melting. Depending on the alloy’s intended use, various levels of aluminum and zinc are added to the molten metal to achieve desired properties. The most common types of aluminum-zinc alloys are ZA-8, ZA-12 and ZA-27. ZA-8 has a higher aluminum content than ZA-12 but lower than ZA-27, so it has better corrosion properties and is more resistant to stress cracking. It can be chrome plated, but is more difficult to machine than the other two alloys.
These alloys have good mechanical properties, but their low creep strength limits their application to temperatures below 150 degC. In order to extend their service temperature range, it is possible to add up to 20 wt.% of silicon (Refs 1, 2, 4, 5, 6) or titanium (Refs 3, 8, 9, 12) to the alloys.
However, these substitutions have the disadvantage of reducing the fluidity and increasing the viscosity, thereby affecting formability during secondary bending, riveting or crimping. Alternatively, partial replacement of Cu with Ti can increase the tensile strength and improve the tribological properties, but reduces the fluidity. Therefore, it is necessary to determine the optimal substitution level.