A good bond between steel and aluminum is possible when steel is first coated with aluminum. This is achieved, for example, by dipping steel plate (steel product) in the aluminum melt. After a few minutes in the melt, an aluminum layer is formed on the steel surface and is metallurgically bonded to the steel. Such a coated steel part can then be placed in a casting mold and cast with aluminum melt.

The process is used in the production of aluminum diesel pistons: the steel ring (reinforcement of the compession ring) is thus treated.

Hi.

You can use another process. Pressing an aluminum bar on surface of stainless steel bar and you can obtained e good adherence between both surfaces. To carried out the process explained before, it is necessary to use turning machine or other process that guarantee height pressure and movement between both surface.

Usually one needs to have a intermediate layer of a third metal/alloy that have good bonding characteristics with both Al and SS, e. g if one does Ni plating on SS ans then bonds with Al it would give better bonding. 

Another thing, it is important to have a certain surface roughness in the stainless steel to ensure a good adhesion.

Thank prof. Vadim

I have tried that method, ie, aluminizing. Even though the ss plates dipped in the molten liquid aluminium, I couldn't get the bonding. I don't know whether oxide layer is forming during diffusion.

Stainless steel forms chromium oxide, which is decomposed in the molten aluminum. Of course, the steel piece has to be kept long enough in the melt to make it hot  and the reaction: Cr2O3 + 2Al = 2Cr + Al2O3 may be runs off. You need a large crucible with aluminum, heated to about 800°C, where you should endure the ss part for about 10 minutes.

For a better and faster wetting of the stainless steel with aluminum melt you can use a flux, for example, euthectic mixture NaCl + KCl + NaF. This flux decomposes not only chromium oxide from the steel surface but also aluminum oxide from the melt.

May be you can try coating Al on SS using solid state techniques such as friction surfacing.