| In this paper, optical microstructure observation?OM?, X-ray diffraction analysis?XRD?, scanning electron microstructure observation?SEM?,energy dispersive spectrometer?EDS?, hot simulation compression test and high temperature tensile mechanical property test were used to investigating the effect of Sn content on the microstructure, hot workability, high temperature tensile properties and high temperature fracture mechanism. The hot workability of as-homogenied ZM61-4Sn alloy was researched by Gleeble-1500 hot simulating compressor, the effects of deformation temperature and strain rate to the flow stress and microstructure were analyzed, the activation energy and stress coefficient were calculated, the constitutive equation of experimental alloys were established, and the thermal processing chart when strain are 0.3 and 0.6 were drew. The high tensile properties of the as-extruded and as-aged ZM61-x Sn?x=0?2?4?6?8?10, wt.%? alloys were tested by electronic universal testing machine, the influence of Sn content on the high temperature tensile properties for the experimental alloys were investigated. The fracture surfaces were observed by scanning electron microscope, and the effect of Sn content on the high temperature fracture mechanism was studied.The results show that: during the hot compression, the as-homogenied ZM61-4Sn alloy has flow characteristics, with the increasing of strain the flow stress increasing first and then decrease gradually until to a steady-state, showing an obvious dynamic recrystallization characteristics. Obtained the material constants of the alloy: the dynamic recrystallization activation energy Q=259.2KJ/mol, stress constant n=12.47, average stress factor ?=0.013, the constitutive equation of the alloy: ·e =7.81×1023[sinh?0.013??]9.602exp?259.2/RT?. Drew the processing map of the alloy at a strain of 0.3 and 0.6, combined the processing map and microstructure analysis obtained the optimal deformation techniques: 320400?, 0.001-0.031s-1.The phase compositions of as-extruded ZM61-x Sn alloys are ?-Mg, ?-Mn, Mg7Zn3,Mg2 Sn and Mg Zn2 phases. Sn element can refine the alloys' microstructure, the average grain size of the as-extruded ZM61-x Sn?x=0?2?4?6?8?10, wt.%? alloys are 15?11?8?5?4 and 3 ?m, respectively. With the increasing of Sn amount, the high temperature strength of experimental alloys increase at first and decrease afterward, ZM61-4Sn alloy has the optimal high temperature properties. The ultimate strength of ZM61-4Sn alloy is 216 MPa, increase 59 MPa than ZM61 alloy, when tensile at 180?. The elongation increasing with the increasing of Sn content, when tensile at 300?, the elongation of ZM61-x Sn?x=0?2?4?6?8?10,wt.%? alloys are 113.8%?183.8%?235.8%?260.5%?258.6% and 265.5%, respectively. The fracture mechanisms of experimental alloys are ductile fracture, and the fracture surfaces were mainly composed of dimples, tearing edge, second phase particles and cavitations. With the increasing of tensile temperature, the morphology of dimples become bigger and deeper, the number of second particles decreases and the number of cavitations increases gradually.The phase compositions of as-aged ZM61-x Sn alloys are ?-Mg, ?-Mn, Mg Zn2 and Mg2 Sn phases. With the increaseing of Sn, the microstructure of the alloys is finer, the average grain size of the as-aged ZM61-x Sn?x=0?2?4?6?8?10, wt.%? alloys are 59, 51, 48, 42, 25 and 19?m. Sn can improve aging strengthening effect, improve the high temperature strength of the alloys, however, the aging strengthening effect would be decrease due to the formation of massive Mg2 Sn phase, the strength of the alloy reach to the maximum, when the weight percent of Sn is 6%. The ultimate tensile strength and yield strength of ZM61-6Sn alloy are 273 MPa and 256 MPa, improve 42 MPa and 49 MPa compared with ZM61 alloy, when tensile at 180?. The elongation of the as-aged alloys decrease with the increase of Sn contents. When tensile at 300?, the elongation of ZM61-x Sn?x=0?2?4?6?8?10, wt.%? alloys are 38.5%?14.6%?13.7%?9.6%?7.9% and 6.9%. The formation of massive Mg2 Sn phase along the grain boundary led to the decrease of grain boundary cohesion, and result in the reduce of high temperature elongation.The fracture surface of ZM61 alloy is mainly composed of cleavage facets, tear ridges and dimples, and the fracture mechanism is transgranular fracture, when tensile temperature range from 180? to 300?. However, the fracture mechanism changed with the addition of Sn, the fracture surface morphology of ZM61-x Sn alloys are mainly composed of tear ridges, dimples and second phase particles.When tensile temperature lower than 220 ?, the fracture mechanism is transgranular fracture, when tensile temperature is higher than 220?, the fracture mechanism is mixed with transgranular fracture and intergranular fracture. |
PDF Full Text Request