Thickness of the degradation layer formed in different media under different conditions (at least 80 points were taken) and the corresponding degradation rate of magnesium (The boxes (bottom to top) show the 25th percentile, median and 75th percentile. The whiskers mark the tenth and 90th percentiles; the rectangular points in the box are average values. Significance levels: ^* p < 0·05, ^** p < 0·01)