Question

Consider the Al-Si phase diagram in the figure below. 1500 B+L Temperature (°C) 500 1.65 12.6 99.83 + B %a = Al 20 40 60 80 si Weight percent silicon What are the percentages of the a-phase and liquid for an Al-5 wt% Si alloy at 578°C? (Enter your answers to two significant figures.) % %L = What are the percentages of a and B phases in this alloy for an Al-5 wt% Si alloy at 400°C? (Enter your answers to three significant figures.) %a = % %B =

Answer 1

Solution: Al- Si Phase Diagram 1500 todo BtL Temperature (och 20 40 60 80 100 120 - Weight percent silicon To calculate percent of d-phase and liquid phase first we shall draw a vertical line from alloy composition of Al-5 wt% Si And at temp. 578° C , a honzontal line is drawn and the intersection point is marked. Now, the percentage of liquid phase is calculated as wt% of liquid - C2-C, C3-C, where C = Percent of silicon in solid phase 2%, C 2 Percent of Silicon in liquid phase : 5% C3 = Percent of Silicon in the alloy =105%.

Calculating the percent for liquid phase: .. Wt. of of liquid - 7 - 1 - ot. % of liquid = 5.5 235.294% - b -15% = 3 = 0.35294 Percent for a- phase : - 100 – 35:294% = 64.706% _ _ Now, at temp. 400°C, a horizontal line is drawn and the intersection point is marked. Now the percentage of a phase is calculated I wt% d-phase - C2-1 - C-C, Here, C = Percent of silicon in solid phase = 4.5% - C₂ = Percent of silicon in liquid phase= 5% C3= Percent of Silicon in the alloy = 29.5% : Wf % of a phase = - we oa phase – 5-4.5 29.5-4.5 - - Dis 0.020 - 2% = 2.000% : Percent of ß - phase = 100-2 =98.000%
Summary: Percent for alpha phase at578℃=35.294% and for liquid phase at 578℃=64.706%.Percent for alpha phase at 400℃=2.000% and for beta phase at 400℃=98.000%.