What about copper container? In this case you could cover it with Gr by CVD. The coating will be continious.

Without an efficient protective layer, most stainless steel types tend to be severely embritled by liquid aluminium at its melting point or above. Chromium resists fairly well to molten aluminium corrosion. Consequently, stainless steel types with high chromium content, as the AISI 446 type with about 25% Cr, can be expected to perform better compared with other grades. Better protection against corrosion can be achieved with a thin layer of chromium deposited over the exposed surface of stainless steels by electroplating.

Grey cast iron resists better to liquid aluminium than most stainless steels or low-carbon steels. That can be attributed to a graphite protective surface layer which remains when iron is initially dissolved by the liquid metal. Some degree of contamination of the molten aluminium by iron can occur. The stress-bearing capability of grey cast iron is quite limited, due to its brittleness.

Besides chromium, both titanium and tungsten resist fairly well to liquid aluminium corrosion. Considering sintered ceramic oxides, both alumina and zirconia also resist well.

You have not indicated the time duration of the exposure and other possibly important aspects of use. Cheap and easy solution could be to use coatings developed for permanent molds (gravity die casting dies). There are 2 types: white coat based on oxides such as Al2O3 and coats based on graphite (maybe you were told about them). They are cheap and can be applied by a regular paint gun (steel needs to be on higher temperature of approx. 300 C - exact temperature depends on actual coating). There are also other solutions, but you need to explain the intended use in more detail (will metals be in contacts for hours or days, how long should coating last, is there any thermal cycling, is thermal inertness a problem - do you require fast change in temperature,...)

Thanks Lazar for the information.

The steel and molten Al are in contact for a few hours and after cooling and solidification of Al, the heating will start the next day. So this is a cyclic process.

Temperature does not change quickly. The coating should last at least for a month!

Hope I answered your concerns.

Thanks,

KE

OK, the sprayed mold coating won't last that long without occasional repair (which is quick and easy as mentioned before) which is troublesome if the Al is always in the steel container (for example if you use it for hot dipping of steel in Al melt).

I once had similar problem - resistance furnace used a steel crucible, but chemical composition of Al alloy did not tolerate high Fe content. I applied approx. 1cm thick castable refractory inside a crucible. Thus I made ceramic crucible inside a steel one which solved the problem for me. In this case, you should be very careful when selecting the thickness. Thermal expansion of steel and ceramics are different and this can lead to failure.

Intermediate solutions with refractory pastes (such as those used for repair of induction furnaces or for heavier insulation of risers in steel molds) is probably also possible (i do not know your geometry and dimensions).

Hope I helped.

I agree with Lazar. 

Furthermore, grphite coating let's say using method such as laser will mostly carburize it making it behave like cast iron on the surface. I have worked with Al and Mg castings. The best bet is graphite or ceramic crucibles.

Regards,

Sameehan

Dear Keivan,

I would check if a diamondlike carbon coating (DLC) could be a sufficient solution.

Enclosed some information about the coating processes and the physical data of such DLC-films...

The costs for this kind of coating seem to be relatively moderate.

With best regards

Michael

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