Effects Of Combined Refiner Modification And Heat Treatment On The Microstructures And Wear Of A356 Alloy

The A356 alloys used in the article were compound refined and modified by adding Al-5Ti-1B-1RE intermediate alloy prepared by self-made fluoride aluminum thermal method as a thinning agent and Al-10 Sr as a modifier, then T6 heat treatment was carried out on the cast A356 and A356 processed by the best compound refinement and modification, and four groups of A356 samples were prepared. The microstructures of A356 alloys compound refined and modified, morphology and distribution of eutectic Si were investigated by Optical Microscope(OM), Scanning Electron Microscope(SEM), Electron Probe Micro analyzer(EPMA) and other modern equipments, and to explore the optimum adding amount of Al-5Ti-1B-1RE as a thinning agent and Al-10 Sr as a modifier. T6 heat treatment was carried out on the cast A356 and A356 processed by the best compound refinement and modification by the box type heat treatment furnace, four groups of samples were prepared, 1# cast A356, 2# A356 of T6 heat treatment state, 3# A356 of compound refinement and modification, 4# A356 of compound refinement and modification state after T6 heat treatment. The mechanical properties and oil sliding wear tests of A356 alloys were tested by tensile machine and the M-2000 abrasion test machine, and to analyze the properties and mechanism of friction and wear.The results show that the microstructures of A356 alloy with 0.8% Al-5Ti-1B-1RE as a thinning agent and 0.3% Al-10 Sr as a modifier added and then carried out by T6 heat treatment were finer, the rounded eutectic Si particles and intermetallic compound distributed evenly around the α-Al phase. The tensile strength σb was 275 MPa, increased 44.7% compared with the cast A356, the elongation was 5.4%, increased 2.6 times, the micro-hardness of α-Al phase was 74 HV, increased 27.6%. The mechanical properties of A356 of compound refinement and modification state after T6 heat treatment was very excellent under the interaction of fine grain strengthening, solid solution strengthening, aging hardening and grain boundary strengthening. Under the same conditions, the wear resistance of cast A356 was the worst, the wear rate and wear amount of per unit time were the highest, while the wear resistance of A356 of compound refinement and modification state after T6 heat treatment was the best, the wear rate and wear amount of per unit time were the lowest. With the increase of load, the wear mechanism of cast A356 was abrasive wearâ†'adhesive wearâ†'serious adhesive wearâ†'delamination wear; while the wear mechanism of A356 of compound refinement and modification state after T6 heat treatment was slight abrasionâ†'micro cutting abrasive wearâ†'abrasion wear â†'abrasive wear+adhesive wearâ†'adhesive wear. The wear rate of A356 of compound refinement and modification state after T6 heat treatment reduced in a certain extent, it was mainly due to fine grain strengthening, solid solution strengthening, grain boundary strengthening and improving the strength and hardness of A356, slowing the softening of grinding surface caused by friction heat, reduce the plastic deformation of sub-surface grinding; Al2O3 particles produced by oxidation during friction the could can play a protective role in the film, it was the first to bear the load, avoiding the α-Al phase and the contact friction of the friction, thus protecting the α-Al phase.