Thermal stress in composite aluminum-steel bar fixed between rigid walls

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wisper
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Before you start going through equations and trying to solve this I just need a simple question answered about this problem.

1) Is it correct for me to assume that the pressure on both walls is equal?

If so, I think the normal stress of the aluminum and steel bars are equal.

Problem:

A circular bar consist of 3in diameter aluminum alloy with Young’s modulus, E = 10,600 ksi, poisson ratio, ν = 0.33, and temperature coefficient, α = 12.5 * 10-6 /°F and 4in diameter steel with Young’s modulus, E = 30,000 ksi, poisson ratio, ν = 0.3, and temperature coefficient, α = 6.6 * 10-6 /°F separated by a rigid piece as shown. The bar is fixed between two rigid end supports and is considered unstressed at 0°F. Determine (a) the normal stress in both the aluminum bar and the steel bar, and (b) the change in diameter of the aluminum and steel bar.

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Since the stresses are inversely proportional to area and Young's, the two members will not have the same stresses.
 
The force is the same through the entire section, but not the pressure.