Microstructure And Properties Of ZA27 Alloy With Micro-alloying And High Intensity Ultrasonic

The ZA27-Mn,ZA27-Si and ZA27-Mn-Si alloys are prepared from ZA27 alloy by adding Mn and Si in the form of Al-10%Mn and Al-7%Si. The solidification microstructures, the morphologies and distributions of the resultant phases are investigated by using Optical Microscope (OM), Scanning Electron Microscope(SEM), Electron Probe Microanalyzer (EPMA) and other modern equipments. The mechanical properties, friction wear properties and thermal expansion properties of ZA27 alloy after adding Mn and Si are tested, and the mechanisms are discussed.The results of microstructure of ZA27 alloy after adding Mn and Si indicate that the element Mn main exist in ZA27 alloy in the form of rich-Mn phase, the optimization amount of Mn is 0.4wt%, the crystal grains are well fined, the precipitated phases are distributed uniformly in the matrix alloy. The morphologies of the Si phase added into the ZA27 alloy in the form of Al-7%Si are particle-shape. When the addition amount of Si is 1.0wt.%, the Si phase is in near ball-shape distributed in the matrix. With the additions of 0.4wt%Mn and 1.0wt%Si, the dendrite crystals are turned into puncheon crystals, and the the precipitated phases are fine in the continuities. With the increase of the ultrasonic power, the dendrite crystals are turn into puncheon crystal, Si particles are fined and distributed more uniformly in the matrix.The mechanical properties tests show that the hardness and tensile strength of the ZA27 alloy with adding Mn and Si increase. When adding 0.4wt%Mn, the hardness, tensile strength and elongation are 126.8HB, 410.32MPa and 4.01%, increased by 9.03%, 8.76% and 22.26% than that of the ZA27 alloy, respectivelity. When the content of Si reach 1.0wt%, the hardness, tensile strength and elongation are 124.9HB, 412.89MPa and3.49%, increase 7.40%, 9.44% and 6.41%, respectivelity. The mechanical properties are improved under different power of the ultrasonic field with 0.4wt%Mn and 1.0wt% Si .The tensile strength, elongation and hardness are all improved. When the power of the ultrasonic field is 1.2kw, tensile strength and elongation are increased by 17.23% and 24.39% compared with the matrix alloy, and by 6.17% and 9.38% compared with adding 0.4wt%Mn and 1.0wt% Si. The change of the hardness is small.The analyse of the SEM of the tensile fracture surface show that the fracture mechanisms are mixed by fracture-the plastic fracture and the brittle fracture.Oil sliding wear tests at room temperature show that the wear resistance of the alloy with Mn adding is superior to that of its matrix alloy. When adding 0.4wt%Mn, the wear weight loss is 0.46mg under 600N load, reduced by 44.58% to the matrix alloy, the friction coefficient is 0.028, reduced by 17.65%, the stability is increased. After adding Si, the resistance of the alloy are improved.When adding 1.0wt%Si into the alloy, the wear weight loss is 0.45mg under 600N load, reduced 45.78% to the matrix alloy, friction coefficient is 0.026, reduced by 23.53% to the matrix alloy, the stability is improved. With the increasing of load, the wear loss weight, friction coefficient are all increased, and the stability decreased. Adding with 0.4wt%Mn and 1.0wt% Si, under different power of the ultrasonic field, with the increasing of the power, the wear loss weigh are reduced, and the friction coefficient reduced, the stability enhanced.The analyse of the wear surface indicates that the wear mechanism is abrasion wear under the oil sliding and low loads conditions. With the loads increasing, the abrasion wear are weakened gradually, and adherence wear increased, in larger load, the wear mechanism is adherence wear and abrasion wear.The results of thermal expansion of alloy show that the liner expansibility and the thermal expansibility of ZA27 alloy are decreased with the adding of Mn. When adding 1.0wt%Si into the ZA27 alloy, the liner expansibility of the material decreased. Adding with 0.4wt%Mn and 1.0wt% Si, the liner expansibility diminish. The ultrasonic field minished the liner expansibility, but its influence is not great.