The Effect Of Mold Cooling Method On The Microstructure And Properties Of Wheel Hub

This paper investigated the effect of different mold cooling method on the product properties of A356.2 casting aluminum alloy.Air cooling mold and water cooling mold were adopted to compare and analyze the obtained microstructure and mechanical properties of wheel hubs.The resulted productivity of different mold cooling methods was also compared.Using well established air cooling and water cooling process parameters,the microstructure and mechanical properties of similar wheel hubs from corresponding molds were studied.The size of α-Al and Si phase was related to the sampling position in wheels from either air cooling or water cooling mold.The decreasing sequence of the size of α-Al and Si phase was the following,center,spoke,inner rim flange,rim and outer rim flange,which was related to the cooling sequence and the cooling rate.The mechanical properties of each part was in the same sequence of the corresponding microstructure as the following,from the strong to the weak,outer rim flange,rim,inner rim flange,spoke and center.When the solidification sequence was the same,compared with the air cooling mold,the cooling rate of the blank was bigger after the aluminum melt entered into the chamber of the mold which was cooled by water due to its higher heat conductivity.The size of α-Al phase was small.The second order dendrite was small and so was the distance in between.The Si phase presented in the shape of short rod.While in the microstructure from the air cooling mold,the second order dendrite was big and the Si phase was in the shape of long rod when compared with those from the water cooling mold.Through comparing the mechanical properties of samples from the same position from the air cooling mold and water cooling mold,it was observed that the tensile strength of wheels from the water cooling mold was 7% higher than that of the air cooling mold and the elongation was 50% higher.The three reliability tests(bending fatigue test,radial fatigue test,13 ° impact test)shown that both the air cooling and water cooling wheel hubs could pass the tests.Both process should satisfy the daily usage requirement.But for the production in a factory,the productivity of the water cooling mold was 25% higher than that of the air cooling mold.This is a great advantage to reduce the cost during production and it is recommended to apply this in a full scale.