I chose the steel for impeller. Production aluminum matrix composite reinforced with ceramic particles by stir casting.
I would expect problems if the steel impeller is in direct contact with molten aluminium. If you have a look at phase diagrams, you'll find intermetallic compounds between Fe and Al, and molten Al is rather reactive. Take this as an example: Difference between cold and warm chamber high pressure die casting machines is that the piston etc. used to press the melt into the mould is immersed in the liquid melt in the warm chamber machines - and while you'll find cold chamber machines for aluminium, to my knowledge you won't find warm chamber ones to process it, one major reason being the difficulty of finding a material that can sustain the working conditions in contact with liquid aluminium. However, I am talking about production machines here: For lab/research equipment, there might be solutions like coatings that would give you not eternal, but sufficient lifetime. To suggest which these might be, I leave to the experts. Wish you luck with your setup and experiments.
I would expect problems if the steel impeller is in direct contact with molten aluminium. If you have a look at phase diagrams, you'll find intermetallic compounds between Fe and Al, and molten Al is rather reactive. Take this as an example: Difference between cold and warm chamber high pressure die casting machines is that the piston etc. used to press the melt into the mould is immersed in the liquid melt in the warm chamber machines - and while you'll find cold chamber machines for aluminium, to my knowledge you won't find warm chamber ones to process it, one major reason being the difficulty of finding a material that can sustain the working conditions in contact with liquid aluminium. However, I am talking about production machines here: For lab/research equipment, there might be solutions like coatings that would give you not eternal, but sufficient lifetime. To suggest which these might be, I leave to the experts. Wish you luck with your setup and experiments.
Dear Dirk
thanks alot
but , can you tell me which materials are suitable for coating ?!
Dear Esmaeil,
It is a general practice to melt aluminum alloys in graphite crucible at lab scale (R&D) because of its inertness to molten aluminum. Nevertheless, a congruent melting phase Al4C3 may form. Therefore, a carbon coating will work for your stainless steel impeller.
Dear Esmaeil,
This is the classic problem with the processing of cast particulate reinforced aluminum MMCs. Molten alumium reacts with all metals. For short times, one may be able to get away with direct contact. However, in your case, you have a multiple issues: long times in contact with molten alumium, abrasive particles and movement that will wear away your coating. With any coating, you will have a CTE mismatch with your impeller and you will not end up with a crack free coating. Softer or more elastic coatings with abrade away quickly. Your only choice is really to go with a ceramic impeller which will increase cost, limit impeller designs which are practical, and require great care in preheating, etc. I think alumina is your best bet. If you must try coating, I'd say that boron nitride is your best bet. There are some ZYP products in an aerosol that provide very good coatings. There is also a BN "Hardcoat" that can be brushed or sprayed on that may be more durable. In all cases, you will need to be careful to limit the speed of your impeller...this is not going to work for a "high shear" impeller. Regards
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