Answer 1

To construct the equilibrium phase diagram and answer the subsequent questions, we need to understand the phase diagram of the Al-Si system. The given data provides information about the solubility limits and eutectic reaction temperature. Here is the step-by-step analysis:

i. Constructing the equilibrium phase diagram: The equilibrium phase diagram for the Al-Si system typically consists of a liquid phase, a solid solution phase (α-Al), and a eutectic phase (α-Al + Si). The eutectic reaction occurs at 12.6% Si and 577 °C. Based on this information, we can plot the phase diagram as follows:

luaCopy code        |       Liquid
        |
        |           +-------- Eutectic (α-Al + Si)
        |           |
        |           |
        |           |
        +-----------|--------- α-Al
                    |
                    |
                    |
                  Composition (% Si)

ii. Composition and relative amounts of phases at various temperatures:

• At 700 °C: Above the eutectic temperature, the alloy will be in the liquid phase.

• At 600 °C: Below the eutectic temperature, but above the solubility limit of Si in α-Al (1%), the alloy will consist of a mixture of α-Al and liquid phases.

• At room temperature (below 500 °C): The alloy will solidify and consist of the eutectic mixture of α-Al and Si.

iii. Percentage of eutectic α-phase (solid solution of Si in Al) for 10% Si - 90% Al alloy: Since the alloy composition is 10% Si and 90% Al, and the eutectic reaction occurs at 12.6% Si, we can conclude that the alloy is hyper-eutectic. In this case, the percentage of the eutectic α-phase will be determined by the lever rule. The lever rule states that the fraction of the α-phase can be calculated using the following formula:

% α-Al = (C - Ce) / (Cs - Ce)

where: C is the composition of the alloy (10% Si) Ce is the eutectic composition (12.6% Si) Cs is the solubility limit of Si in α-Al (1%)

Substituting the values:

% α-Al = (10 - 12.6) / (1 - 12.6)

% α-Al = -2.6 / (-11.6)

% α-Al ≈ 22.41%

Therefore, the percentage of eutectic α-phase in the 10% Si - 90% Al alloy is approximately 22.41%.

iv. Cooling and microstructures: The cooling and microstructures of the alloy can be represented as follows:

• Cooling from above the eutectic temperature:

• At the eutectic temperature (577 °C), the alloy will start to solidify, forming a mixture of α-Al and liquid phases.

• Upon further cooling, the α-Al phase will continue to solidify until reaching room temperature, forming a solid solution of Si in Al.

• Microstructure at room temperature:

• At room temperature, the microstructure will consist of a matrix of α-Al with dispersed Si particles, forming the eutectic structure.

Please note that the above information is based on the given data and assumptions made for the Al-Si system. Actual phase diagrams and microstructures may vary based on specific alloy compositions and processing conditions.