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Nonferrous metals and alloys

Check aluminum alloy series and tempers, GP zones and overaging, clad sheet, Al-Li alloys, tough-pitch copper and copper spring alloys, magnesium alloy designations and corrosion, titanium alloy microstructures and the Ni-based alloy 718 with multiple-choice questions.

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Nonferrous metals and alloys: key points

Aluminum alloys are at the center of nonferrous materials. For wrought alloys, the thousands digit of the four-digit number indicates the main alloying element, and temper designations such as O, H and T indicate the state of working and heat treatment. The 2000, 6000 and 7000 series are strengthened by solution treatment and aging, through precipitation that proceeds from GP zones via intermediate phases to the equilibrium phase, and overaged tempers are used to change the balance between strength and corrosion resistance. To make use of lightness, comparisons should use specific strength, specific stiffness or an index suited to the shape of the part.

Copper has a high electrical conductivity, and oxygen-bearing tough-pitch copper and oxygen-free copper are chosen according to the application; for springs, phosphor bronze strengthened by solid solution and work hardening and precipitation-hardened beryllium copper are used. Magnesium alloys, the lightest structural metals, require attention to corrosion by local cells formed by impurities. Titanium alloys are given different microstructures through working and cooling conditions, and Ni-based alloys keep their strength to high temperatures through precipitation of γ' and γ''.

All Nonferrous metals and alloys questions (15)
  1. Which is the correct pairing of the thousands digit of the four-digit designation of wrought aluminum alloys with the main alloying element?
  2. In the ASTM designation system for magnesium alloys, what does “AZ91,” widely used for die casting, stand for?
  3. Among the temper designations of aluminum alloys, what does “H34,” used for alloys such as 5052, stand for?
  4. 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?
  5. 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?
  6. 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?
  7. 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?
  8. Suppose that adding lithium to aluminum lowers the density by about 3% and raises Young's modulus by about 6% per mass% of Li. About how many times that of pure aluminum is the specific stiffness (Young's modulus/density) of an Al-Li alloy containing 2.0 mass% Li? Assume the changes are proportional to the amount added.
  9. Tough-pitch copper (copper containing about 0.02 to 0.05% oxygen, mostly dispersed as Cu₂O) can become brittle when it is heated in a reducing atmosphere containing hydrogen or is gas welded or brazed. Which gives the correct cause and remedy?
  10. Among copper alloys for springs and connectors, which is the correct pairing of the strengthening mechanisms of phosphor bronze and beryllium copper?
  11. The corrosion resistance of magnesium alloys depends strongly on the amounts of the impurities Fe, Ni and Cu, and in high-purity alloys such as AZ91D the upper limits for Fe and Ni are set very low, at about 0.005% or less. Which is the correct reason?
  12. A flat panel whose thickness is chosen to give a fixed bending stiffness is changed from an aluminum alloy (Young's modulus 70 GPa, density 2.70 g/cm³) to a magnesium alloy (Young's modulus 45 GPa, density 1.74 g/cm³). If the area of the panel is the same and the bending stiffness is proportional to E × (thickness)³, about how many times the mass of the aluminum alloy panel is the mass of the magnesium alloy panel?
  13. In α+β titanium alloys such as Ti-6Al-4V, cooling from above the β transus gives a lamellar structure of colonies of plate-like α, while working below the β transus and annealing gives a structure containing equiaxed α. Which statement about the difference in properties between these two structures is correct?
  14. In designing α and α+β titanium alloys, the effect of α-stabilizing elements is summarized by the aluminum equivalent [Al]eq = [Al] + [Sn]/3 + [Zr]/6 + 10[O] (mass%), with a guideline that it should not exceed about 9. For a Ti-6Al-2Sn-4Zr-2Mo alloy containing 0.10 mass% oxygen, which is closest to [Al]eq?
  15. The Ni-based alloy 718 (a Ni-Cr-Fe alloy containing about 5% Nb) is widely used for jet engine disks and similar parts. Which statement about its strengthening and characteristics is correct?

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