A chrome pickle treatment for magnesium. Color varies from matte gray to yellow-red. Only fair corrosion resistance (less than 24 hours 20% salt spray resistance).

A dichromate treatment for magnesium. Color varies from light brown to dark brown to gray depending on alloy. Only fair corrosion resistance (less than 24 hours 20% salt spray resistance).

An electromagnetic steel sheet has an electrically insulating coating with superior weldability, formed by coating a treatment solution on the electromagnetic steel sheet and baking the same, the treatment solution containing a synthetic resin fine-particle emulsion having resistance against chromic and/or bichromic acid and exhibiting a peak temperature not lower than 400.degree. C. at which a weight change rate is maximized when a sample is heated at a constant rate in differential thermal gravimetry, a chromate and/or bichromate base aqueous solution containing at least one kind of two-valence metal, and an organic reducer. The steel sheet is superior in electrical insulation, adhesion, punching ability, weldability and corrosion resistance.