This link may help. Scroll down to 9.2:
http://www.intechopen.com/download/get/type/pdfs/id/12757Also, if you have access to Volume 4, Seventh Edition of the Welding Handbook, published by the AWS, there's information on brazing magnesium alloys.... pre-braze cleaning, furnace brazing, torch brazing, dip brazing, and post-braze cleaning.