Influences Of Different Types Of Foundry Returns On The Quality Of Wheels

The article considers A356.2 cast aluminum alloy as the study object,and aims at thoroughly investigating the influences of the pure aluminum ingot,100% waste wheel and 100% aluminum scrap foundry returns on the properties of low pressure cast products,by analyzing and comparing the chemical composition,microscopic structure,refinement and modification effects,mechanical properties and reliability of the acquired hub blanks,which has played a guiding role towards actual production.By focusing on the similar wheel types,the article has carried out quality assessment on the acquired aluminum liquid corresponding to different raw materials by applying matured and the same smelting process.It can be concluded through the comparison that,whether it is pure aluminum ingot,waste wheel,or the aluminum liquid melted from aluminum scraps,their chemical compositions have all been within the scope according to the process requirement,in which,the contents of Ti and Sr have the greatest changes,the contents of Ti and Sr in the waste wheel are relatively higher,and the elemental compositions in aluminum scrap liquid have been generally lower than other two.The density of aluminum liquid inside the aluminum scrap furnace is extremely low,whereas the density of aluminum ingot liquid is satisfactory.Aluminum liquid melted from pure aluminum ingots has the best fluidity,whereas aluminum scrap liquid has the worst fluidity.All three kinds of aluminum liquid have similar refinement and modification capabilities,in which,the waste wheel has the better refinement and modification capability than the other two.After the three kinds of different aluminum liquid being sampled in the furnace and through metal impurity inspections,the 100% aluminum ingot liquid has the lowest impurity content,and the 100% aluminum scrap liquid has the highest impurity content;however,after being refined,all three kinds of aluminum liquid have almost the same impurity contents.Aluminum ingot liquid has the highest rate of finished products,whereas the aluminum scrap liquid has the lowest rates,the major defects of which are shrinkage porosity and cinder inclusion.The main reason is that,while being smelted,the residue content of aluminum scrap liquid is large;after being refined,the residue bulks can be removed,and it is not easy to remove residues with diameters below 20?m.These remaining residues suspend inside the aluminum liquid,and keep growing;they will enter into the wheel hubs along with the aluminum liquid inside the heat insulation furnace for die casting machine,which will result in scrapping.Shrinkage and porosity have been caused mainly by the poor fluidity of aluminum scrap liquid and insufficient feeding capacity.When using aluminum scrap liquid,small slag can be obviously observed in the microscopic structure sampled from the wheel hub.These slag have been distributed not only on the crystal boundary(namely at the crumby eutecticum),but also between secondary dendrite arms;few slag can also be wrapped into the crystal by primary ?-Al.As for the wheel hubs corresponding to all three kinds of aluminum liquid,the microscopic structure of aluminum ingot liquid is dense and defect-free;therefore,it has the optimal mechanical properties.The aluminum scrap liquid has the worst properties.Due to the existence of slag,the deformation of slag is inconsistent with that of the primary structure during tensile deformation,which results in the easy generation of micro holes at the joining points of slag and the primary structure;with the growing of the holes,the crack source will be created,which leads to abnormal fracture in the end.As being indicated by the three major reliability tests on wheel hubs(bending fatigue test,radial fatigue test,and 13° impact test),wheel hubs produced from three kinds of aluminum liquid are qualified through bending and radial fatigue tests,whereas the wheel hub produced from aluminum scrap liquid fails the impact test.According to the fracture,the major failure cause is the influence by inclusions.