| In this paper, effects of Zn and Ce content on the microstructure and mechanicalproperties of Mg-Zn-Mn-Ce alloys were studied. The as-cast and as-extruded alloys ofdifferent Zn contents (1.0%,1.5%,2.0%,2.5%) and Ce contents (0.1%,0.7%) wereobtained by melting and extrusion tests. The effect of small changes of Zn contents onthe microstructure and mechanical properties of Mg-xZn-Mn-0.5Ce alloys was studied,and the mechanism was analyzed; the microstructure and performance of low Cecontent Mg-2Zn-Mn-0.1Ce (1#) alloys and high Ce content Mg-2Zn-Mn-0.7Ce (7#)alloy under different extrusion temperatures were compared and analyzed. The opticalmicroscopy (OM), scanning electron microscopy observations (SEM) and quantitativemetallographic analysis, and XRF, DSC, XRD, micro-hardness, tensile properties atroom temperature and other characterization of methods were used, in order to optimizethe composition of the alloys and hot extrusion process parameters, achieved thefollowing results:(1) With the increase of Zn content, the recrystallized grain sizes ofMg-(1.0~2.5)Zn-Mn-0.5Ce alloys decreased from3.8μm to3.0μm, reduced in a smallextent; The proportion of non-recrystallized tissue increases and the uniformity of tissuedecreased; The species of the second phase has not changed, but the number graduallyincreased. During the extrusion process, the second phase of the alloy was crushed anddistributed along the extrusion direction (ED).(2) With the increase of Zn content, yield strength and tensile strength of extrudedMg-(1.0~2.5) Zn-Mn-0.5Ce alloy increase a little, and the elongation increases at firstand then dicreases. When the content of Zn is1.5%, the mechanical properties of thealloy are optimal with yield strength243.1MPa, tensile strength287.3MPa andelongation18.1%.(3) Under different extrusion temperature, average sizes of1#(Mg-2Zn-Mn-0.1Ce)alloy and7#(Mg-2Zn-Mn-0.7Ce) alloy which have different Ce content are all smallthan5μm. At the same extrusion temperature, refining effect in thermal deformation of7#alloy is better than1#alloys. With the increase of extrusion temperature, the averagegrain size of the two alloys are all have the trend of increase, while the unrecrystallizedarea is significantly reduced. At340℃, the grain size of the1#alloy is only1.6μm.With the extrusion temperature rise to430℃, the grains of the alloy had grown to 3.9μm; the grain size of7#alloy grew up from1.3μm to2.9μm.(4) In1#alloy, the second phases were very rare, dispersed in the matrix in form offine particulate. With the extrusion temperature increase, the number and thedistribution of the second phases of the1#alloy did not changed significantly. Therewere streamlined crushed second phase particles along the direction of extrusion in7#alloy. As the extrusion temperature increase, portion of the second phase particlesdissolved into the matrix, distributed more and more diffused. After extrusion throughdifferent temperatures of the same alloy, the kinds of second phases had not changed.(5) With the extrusion temperature growing up from340℃to430℃, change of theyield strength, tensile strength and hardness values of the two alloys were identical, aslight downward trend were tested. Elongation were all increased first and then declined.And the elongation of the1#alloy and7#alloy reached a peak at370℃and400℃respectively. The yield strength of1#alloy was higher than250MPa, tensile strength290MPa, elongation20%. Continue to adding more Ce to the alloy, strength andplasticity of7#alloys obtained only limited improvement, so when attention the cost ofraw materials alloy, the Ce content of1#alloy was easier to accept for commercialpurposes. |
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