EFFECT OF Mn AND Mg ON THE MORPHOLOGY OF PRIMARY Al_3Fe PHASE IN Al-5Fe ALLOY
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Adding Mn and Mg in Al-5Fe(mass fraction, %) alloy has obvious effect on the morphology of the primary Al3Fe phase which is thick needle plate-like before adding alloyed elements. The addition of 2.5% Mn and 0.1% Mg(mass fraction) changes the primary Al3Fe phase from thick needle plate-like to fine needle-like, particle-like and flower-like; the additon of 2.5% Mn and 1.5% Mg forms particle-like and fringe-like (bifurcated), the forming mechanism of which was analysed. The mechanical property is raised after the addition of Mn and Mg: the tensile strength of Al-5Fe alloy is 107 MPa, Al-5Fe-2.5Mn-0.1Mg alloy 139 MPa and Al-5Fe-2.5Mn-1.5Mg alloy 122 MPa. The properties are increased by 29.9% and 14% respectively compared with that of Al-5Fe alloy.Keywords:
Mass fraction
Morphology
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In order to improve the high-temperature strength of an Al-Cu-Mg alloy, Mn was added at supersaturation to form a high-density dispersion of an intermetallic phase. In the P/M Al-3.6Mn- 6.4Cu-3.6Zn-1.7Mg alloy (mass%), rod-like Al-Mn-Cu-Zn quaternary intermetallic phases (Q phase) several hundred nanometers in length were dispersed in the matrix. The chemical composition of the Q phase was determined by TEM/EDX to be 78.8Al-12Mn-8Cu-1.2Zn (at%). The crystal system, space group, and lattice parameters of the unit cell were identified to be orthorhombic, Cmcm and a = 0.76, b = 2.11, c = 1.25 nm, respectively, by Rietveld analysis. Since the matrix of the alloy obtained was of the Al-Cu-Mg-(Zn) system, age-hardening occurred by formation of a GPB zone at room temperature and 448 K. At the peak level of age-hardening at room temperature, the tensile strength at room temperature was 704 MPa, and the elongations were 8.0%. The high temperature strengths at 523 and 573 K were 319 and 141 MPa, respectively, and the elongations were 17 and 34%, respectively.
Orthorhombic crystal system
Precipitation hardening
Rietveld Refinement
Hardening (computing)
Lattice constant
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Solid solution strengthening
Precipitation hardening
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Thermal Stability
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An Al-20Mg-4Si high Mg containing alloy has been produced and its characteristics investigated. The as-cast alloy revealed primary Mg2Si particles evenly distributed throughout an α-Al matrix with a β-Al3Mg2 fully divorced eutectic phase observed in interdendritic regions. The Mg2Si particles displayed octahedral, truncated octahedral, and hopper morphologies. Additions of Sb, Ti and Zr had a refining influence reducing the size of the Mg2Si from 52 ± 4 μm to 25 ± 0.1 μm, 35 ± 1 μm and 34 ± 1 μm respectively. HPDC tensile test samples could be produced with a 0.6 wt.% Mn addition which prevented die soldering. Solution heating for 1 hr was found to dissolve the majority of the Al3Mg2 eutectic phase with no evidence of any effect on the primary Mg2Si. Preliminary results indicate that the heat treatment has a beneficial effect on the elongation and the UTS.
Elongation
Tensile testing
Morphology
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Microstructure and corrosion behavior of the Mg-3Al-xMn (x = 0, 0.12, 0.21, 0.36, 0.45) (hereafter in wt.%) alloys were experimentally investigated by electron probe microanalysis (EPMA), scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electrochemical, and hydrogen evolution tests. A new self-constructed Mg-Al-Mn-Fe thermodynamic database was used to predict the solidification paths of the alloys. The addition of Mn showed no grain refinement in the cast Mg-3Al alloys. According to the microstructure observation, Al-Fe phases were observed in the non-Mn-added alloy, while Al8Mn5(LT) (Al8Mn5 in low temperature) became the main intermetallic phase in the Mn-added alloys, and the amount increased gradually with the Mn addition. The τ–Al0.89Mn1.11 phase with lower Al/(Fe + Mn) ratio was observed in the alloys with 0.36 and 0.45 wt.% Mn content. According to the electrochemical tests, all five alloys showed localized corrosion characteristics in 3.5 wt.% NaCl solution. Compared with the Mg-3Al alloy, the corrosion resistance of Mn-added alloys were significantly improved and increased gradually with the Mn addition, which was due to the variation of Al-containing intermetallic compounds. The present experimental investigations and thermodynamic calculations confirmed the mechanism that the increasing amount of Al8Mn5(LT) with Mn addition could encapsulate the B2-Al(Mn,Fe) phase with higher Fe. Therefore, it could prevent this detrimental phase from contacting magnesium matrix, thus suppressing micro-galvanic corrosion and improving corrosion resistance gradually.
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The microstructure of Al-7Si-0.4Mg-1Fe alloy mainly consists of aluminum dendrites, Al-Si eutectics, and needles. When Mn was added to the alloy, the substantial amount of phase was changed into Al(Mn,Fe)Si, however the needle-like morphology was almost unchanged. Combined additions of Cr or Sr with Mn to the base alloy resulted in rod-like Al(Mn, Fe,Si)Si phase. The tensile properties of as-cast alloys were enhanced by the Mn addition, especially when it was added with Sr. The tensile properties after T6 heat treatment was a little improved with 0.7%Mn addition, but Cr or Sr additions with Mn didn't show any positive effect on the properties of heat-treated alloys.
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Microstructure and aging hardness variation of Al-Mg-Si alloys with different Mn or Fe content were investigated to reveal the effect of Mn or Fe on the age hardening behavior of Al-Mg-Si alloy using transmission electron microscopy. The peak hardness of the alloys with small content of Mn or Fe is higher than that of the base alloy; the peak hardness of the alloy with 0.2at.%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25at.%Mn is lower than that of the base alloy. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25at.%Mn or 0.2at.%Fe.
Hardening (computing)
Precipitation hardening
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Mg-xLi-Al alloys with Mn addition from 0.2% to 1.5 % by wt. were produced and studied. The density of the alloys is very low, between 1.21 g/cm3 and 1.64 g/cm3, while the microstructures change from single α-, (α+β)-, to single β-phase with lithium content rising from 5 % to 22 % by wt. The main alloy studied was LA92 alloy with Mn addition. The results of the tensile tests show that the strength decreases with increasing lithium content, while the elongation increases sharply, and the UTS and YS rise by 26.8% and 22.7% respectively, when 0.5 % by wt. Mn is added. It is also known, by microstructure observation, SEM with EDS and X-ray analysis, that adding Mn can produce some new hard phases in the alloy, which may worsen the tensile properties.
Elongation
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