From the Machinery's Handbook, 23rd Ed., p. 398, the Coefficients of Thermal Expansion for Aluminum and Steel.

metal	coef. of thermal expansion
Aluminum	12.44 uin/in deg F
Carbon Steel	6.33 uin/in deg F

(uin is micro inch; 1,000,000 uin = 1 in).

Clearly, if you've got steel inserts in aluminum (bearing races in hubs, for example) the use of heat to remove the steel insert without removing aluminum material is essential to overcome, or at least reduce, the interference fit.

For example, a bearing race 1.5 inches in diameter installed in aluminum with a 0.0018 inch interference fit will be ready to fall out if the assembly is heated by 200 deg F. Upon reinstallation, the room temp bearing races will go in if the temperature of the aluminum is raised by 100 deg F (at least until the bearing races pick up some heat from the aluminum, anyways). I have no idea, however, if this is a plausible number for the interference fit.