The influence of aluminum tri-polyphosphate on the protective behavior of Mg-rich epoxy coating on AZ91D magnesium alloy

► Aluminum tri-polyphosphate (SAP) pigment is added in a Mg-rich epoxy coating. ► SAP improves anticorrosive performance of the Mg-rich coating on AZ91D alloy greatly. ► SAP prolongs cathodic protection of Mg-rich coating by a pH buffering effect. ► The formed phosphates and oxides of Mg strengthen the barrier effect.