The semi-solid rheomolding AZ91D auto tire active safety device parts were prepared.The effects of severe rolling friction on the semi-solid rheomolding AZ91D auto parts were analyzed by "the fatigue experiment" and "25 000 km road test of cars equipping with the sample parts" and "50 km road test of cars after sudden deflation of their tires".The results indicate that the heat generated by the severe rolling friction can increase the temperature of the parts sharply to increase the plasticity of the parts

which is responsible for the strain accumulation and shading holes at the crack tip of the semi-solid rheomolding AZ91D auto parts.Someα-Mg phases in the transient zone can be torn into thin strips about 110 nm in diameter or 31 nm sheets.The heat can cause the remelting of β-Mg

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of the eutectic structure in the surface layer of the parts local firstly

and the molten liquid flows along long cracks at the fracture

so the content reduction of eutectic structure between the adjacentα-Mg phases can result in gaps of 700 to 2 700 nm.The hardness of part which failed at 36 km in the road test of cars after sudden deflation of their tires is decreased by 9.6%

and the maximum hardness position is moved 1 mm into the part

which are attributed to structure change in the surface layer and the high temperature annealing.