Plating to make aluminum magnetic

A. You might look into how hard disks are manufactured, Andrea, since they sound very similar to what you're looking for. They have been done at least three ways, iron oxide applied to the aluminum platter, electroplated magnetic coatings, and sputtered magnetic thin films.

A. Sorry, I have no knowledge of that process, Andrea, but I think you should be able to find some info on how the magnetic tape used in VCR recorders, voice recorders, and the magnetic strip on the back of credit cards is made.

A. Try plating the aluminium with nickel or cobalt. You will need to do a zincate pretreatment first, otherwise it won't adhere. Both nickel and cobalt are magnetic, but not as magnetic as iron. Alternatively, try vacuum deposition of iron, nickel or cobalt etc.

A. Andrea, firstly, make sure the aluminium is suitable for electroplating - some alloys do not bond well to any electrodeposit.

Secondly, I would strongly recommend you get a proprietary zincate solution and follow the suppliers instructions on how to prepare the aluminium for the zincate treatment. Failure of the zincate process will certainly result in electroplating failure, so make sure you get this right. The pretreatment will include etching and desmutting, but be determined by the type of aluminium you are using. It will need etching and desmutting, but the process details will be determined by the alloy.

Once zincated, you can put down the nickel or cobalt. I would suggest you use nickel, because it is cheaper and much better known. There are numerous reports that say cobalt plating is the same as nickel plating and I would strongly disagree with this; cobalt plating is much more complex and difficult to achieve. If you do use nickel, you can either use a high sulphate nickel, a Watts nickel or a sulphamate nickel. The best two options are Watts and sulphamate, but if you use Watts, substitute the nickel chloride with nickel bromide. This is because aluminium is very susceptible to chloride attack and bromide is much more benign, but still does the job in helping anodic polarisation. If you use sulphamate, you don't need chloride in the solution, as you should use sulfur depolarised nickel anodes.

Once nickel plated, the aluminium artifact will be magnetic. Since you want to plate the nickel with gold, make sure there are no organic brighteners and levelers in the nickel solution, as this can cause adhesion problems for the gold. If you must use additives, you will need to give the nickel a very short etch before gold plating, otherwise the gold may suffer from poor adhesion. I have no experience of neodymium plating so cannot comment on it.