English
Menu

Nonferrous metals and alloys

In the ASTM designation system for magnesium alloys, what does “AZ91,” widely used for die casting, stand for?

  1. AAn alloy whose main additions are Al and Zn, with about 9 mass% Al and about 1 mass% Zn
  2. BAn alloy whose main additions are Al and Zr, with about 9 mass% Al and about 0.1 mass% Zr
  3. CAn alloy whose main additions are Zn and Al, with about 9 mass% Zn and about 1 mass% Al
Show answer and explanation

Answer: A. An alloy whose main additions are Al and Zn, with about 9 mass% Al and about 1 mass% Zn

In the ASTM system the two main alloying elements are given one letter each in decreasing order of content (A for Al, Z for Zn, M for Mn, K for Zr, E for rare earths, W for Y and so on), and the numbers that follow are their rounded mass percentages. AZ91 contains about 9% Al and about 1% Zn, and a final letter, as in AZ91D, distinguishes stages of improvement such as tighter control of impurities. The letter for Zr is K, so reading Z as Zr is wrong. The numbers follow the order of the letters, so reading Zn as 9% is also wrong. Al raises strength through solid-solution strengthening and the formation of Mg₁₇Al₁₂ during solidification and precipitation, and it improves fluidity and castability, but too much lowers ductility. AZ31 (about 3% Al and about 1% Zn) is commonly used for wrought products.

Report an error

Practice this topic Back to topic

More Nonferrous metals and alloys questions

  1. Among the temper designations of aluminum alloys, what does “H34,” used for alloys such as 5052, stand for?
  2. Consider why aluminum is used for overhead power lines by comparing the masses of conductors of the same length and the same electrical resistance. Taking the conductivities as 61% IACS for aluminum and 100% IACS for copper, and the densities as 2.70 g/cm³ for aluminum and 8.96 g/cm³ for copper, about how many times the mass of the copper conductor is the mass of the aluminum conductor?
  3. Sheet of alloys such as 2024 used for aircraft skins is often supplied as clad sheet (Alclad), with thin layers of pure aluminum or an Al-Zn alloy roll-bonded to both faces. Which is the main role of these layers?
  4. When an Al-Cu alloy is solution treated, quenched and aged, the precipitates change roughly in the sequence GP zones → θ'' → θ' → θ (Al₂Cu). Which statement about GP zones is correct?
  5. For thick plate and forgings of alloy 7075, the overaged T73 temper is sometimes chosen over T6, which gives the highest strength. Which is the main reason?