Question

Zinc percentage in alpha - brass is

• A. 0 - 50
• B. 45 - 50
• C. 0 - 36
• D. above 58

Hint:

Remember that alpha-brass is essentially copper with zinc dissolved in it. Common alpha brasses include Cartridge Brass (70

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question relates to the Copper-Zinc (Cu-Zn) phase diagram, which describes the different phases of brass alloys. Alpha-brass (\(\alpha\)-brass) is a specific phase in this system. We need to identify its composition range in terms of zinc percentage.

Step 2: Detailed Explanation:
Alpha-brass (\(\alpha\)-brass) is a solid solution of zinc dissolved in the FCC crystal structure of copper. According to the Cu-Zn phase diagram:

• The alpha phase exists from pure copper (0% Zn) up to the solubility limit of zinc in copper.

• This solubility limit is not constant but changes with temperature. The maximum solubility is about 39% Zn at 456°C. At room temperature, the solubility limit is lower, around 35-36% Zn.

• Brasses with more than \(\approx\)36% Zn will contain another phase, the beta phase (\(\beta\)-brass), in addition to the alpha phase at room temperature (these are called duplex or alpha-beta brasses).
Therefore, the region for single-phase alpha-brass extends from 0% zinc up to approximately 36% zinc.
Let's check the options:
(A) 0 - 50: Incorrect. Above \(\approx\)36%, other phases appear.
(B) 45 - 50: This range corresponds to beta or gamma brasses, not alpha-brass.
(C) 0 - 36: This correctly represents the composition range for single-phase alpha-brass.
(D) above 58: This corresponds to gamma or epsilon brass phases.

Step 3: Final Answer:
The zinc percentage in single-phase alpha-brass ranges from 0% up to a maximum of about 36%.