Electrolysis of aluminum in a solution of magnesium sulfate
Aluminum is not a good idea for carrying out electrolysis, because this metal is covered by a thin layer of aluminum oxide (or alumina) that is insulating. The current passing between these electrodes must be really weak, because the resistance of this layer is high. So that you need a high tension to break this layer and make an electrolysis. But, as soon as aluminium is in contact with water, a new aluminum layer is formed. The majority of the electric energy is wasted and lost for heating the solution. This is non-sense. The powder that you get is probably aluminum oxide coming from the broken alumina layer I told you about earlier. And magnesium is not involved in this reaction.