| In order to develop a new magnesium alloy with high electromagnetic shielding efficiency for electronic-controlled box, new Mg alloy of Mg-7Al-lZn-0.3Mn-0.9Y-0.6Ce based on Mg-Al-Zn was made by adding Y and Ce element with different contents through a common casting process. Using an optical microscope (OM), scanning electron microscopy (SEM), X-ray tester (XRD) analysis of the microstructure of the alloy prepared.With the conductivity meter, flange coaxial tester, Brinell hardness tester, universal testing machines and other electronic means of testing for the alloy prepared electromagnetic shielding performance and mechanical properties were studied Y, Ce alloy elements on the microstructure. mechanical performance and electromagnetic shielding effectiveness, optimizing the heat treatment process of the alloy.The proper amount of rare earth Y, Ce was added to the alloy, which can significantly improve the alloy microstructure. The second phase is becoming massive and dispersed particles shape from relatively coarse dendrite mesh, with a square block of Al2Y phase, needle Al4Ce phase being generated, which had had a significant refinement to the organization. The organization was refined well by a phase matrix refinement, the transition of second phase from coarse dendrite mesh to dispersed bulk and granular crystal, as well as the formation of massive Al2Y phase and needle Al4Ce phase. When the amount exceeds a certain amount, alloy was coarsening with the gradually increasing of the amount. When the addition of Y or Ce exceeded a certain amount, alloy structure was coarsening with the gradually increasing amount. Its mechanical properties were optimized when the amount of Y or Ce was 0.9 wt%. Combined addition of Y and Ce have a greater impact on the microstructure and mechanical properties of the alloy microstructure. Under the combined action of precipitation strengthening of Al2Y and Al4Ce phase, grain refinement strengthening of Y and Ce. the mechanical properties of the alloys have been significantly increased. Ce-cast Mg-Al-Zn alloy can obtain better mechanical properties by adding 0.9wt% Y-0.6wt%Ce, with its tensile strength of 218MPa, elongation 10.5%. and HB hardness 69.86.Alloy can have a good shielding effectiveness by adding Y, Ce alloying elements. Alloy has the best shielding effectiveness when its contains 0.9wt% Y,0.6wt% Ce, with the highest shielding effectiveness value of 108.3 dB at 25 MHz, and the lowest value 87.13 dB at 1495 MHz, which can meet military requirements of 60-120dB. Rare earth elements Y, Ce can improve the conductivity and shielding effectiveness of Mg-Al-Zn alloy for the newly formed Al2Y, Al4Ce phase. Solid solubility of Al in Mg can be reduced by adding proper Y and Ce to refine the alloy, so that the alloy conductivity and electromagnetic shielding effectiveness are improved. Excess rare earth element will increase the formation of compounds, reduce the grain size, and increase the grain boundary. The scattering of electrons was increased and the conductivity was decreased, which affected the electromagnetic shielding effectiveness.The dispersed β-Mg17Al12 phase will dissolve after the solid solution of Mg-7Al-1Zn-0.3Mn-0.9Y-0.6Ce alloy, while it will precipitate after aging. When the aging temperature increased from 150℃ to 200℃, continuous β-Mg17Al12 precipitates increased. With the aging time passing, the number of β-Mg17Al12 increases and the proportion of continuous precipitation phase is increasing too which result in gradually increase of the tensile strength and hardness values, but decrease of elongation of alloys. It is ultimately determined that the best heat treatment process for casting alloy is solid solution after 415℃ x 12h at 80 ℃ warm water quenching and aging 200 ℃ by 12h, air cooling.The tensile strength increases to 243MPa, Brinell hardness reaches 75.2HB, and elongation becomes 12.3%. After heat treatment, the alloy can meet the demand of mechanical standard for electronic control box material. |
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