From the home of vapour / vapor / wet / aqua / hydra / hydro blasting. So many variations of a title for the same basic process lol !!!
When I do magnesium for customers parts the paint is removed in a methylene chloride dip tank then vapour blasted at a reasonably high pressure for paint prep, along with another little trick which gives a little more 'key' for paint to latch onto unless it is going to be left unpainted and then it's done with a different approach for a more durable and dressy finish.
Magnesium should generally be painted for maximum protection as it can be more unstable and vulnerable to corrosion.
Same process applies for aluminium but for a dollar reason. Why spend your dollars for me to chase a shiny finish that paint is less likely to want to attach too.
Hope this helps.
Dave Mac