The GATE Grind

GATE 2025 MT – Question 28

Physical Metallurgy · Heat treatment and recrystallization · 1 mark · Multiple select

Which of the following statements is/are CORRECT with respect to the initial stage of GP zone formation in a precipitation hardenable Al - 4.5 wt.% Cu alloy?

  1. GP zones are Cu-rich clusters.
  2. GP zones are CuAl2 precipitates.
  3. GP zones are incoherent with the matrix.
  4. GP zones are coherent with the matrix.

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Show answer and explanation

Correct answer: (A) GP zones are Cu-rich clusters.; (D) GP zones are coherent with the matrix.

Explanation

Early GP zones are Cu-rich clusters retaining coherency with the aluminium lattice. They precede the later precipitate sequence and are not the equilibrium stoichiometric CuAl2 phase. Thus **A,D** are correct; describing them as incoherent is inconsistent with this initial stage.