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Nonferrous metals and alloys

Among the temper designations of aluminum alloys, what does “H34,” used for alloys such as 5052, stand for?

  1. ASolution heat-treated, cold-worked and artificially aged, with the hardness adjusted to 40% of the hardest state
  2. BStrain-hardened and then partially annealed, with the hardness brought back to three quarters of the hardest state
  3. CStrain-hardened and then heated at low temperature to stabilize the properties, with a hardness midway between O and the hardest state
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Answer: C. Strain-hardened and then heated at low temperature to stabilize the properties, with a hardness midway between O and the hardest state

H denotes strain-hardened material; the first digit indicates the treatment after working and the second the degree of hardness. H1x is strain-hardened only, H2x strain-hardened and then partially annealed, and H3x strain-hardened and then stabilized by low-temperature heating. A second digit of 8 is the hardest state, 4 is half-hard, midway between O (annealed) and 8, 2 is quarter-hard and 6 three-quarter-hard. 5000-series alloys with high Mg contents gradually soften and change their properties when kept at room temperature, so H3x tempers, given a low-temperature heating in advance to stop this, are used. Solution treatment and aging are treatments of the T tempers of heat-treatable alloys and are not applied to the non-heat-treatable 5052. Partial annealing is H2x, and a second digit of 4 means half-hard.

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