Grain Refinement Of Mg Research Articles

The role of Al2Y in grain refinement in Mg–Al–Y alloy system

A series of Mg–10(Al + Y) alloys with various weight ratios of Al to Y were cast to investigate the role of Al2Y in grain refinement in Mg–Al–Y ternary system. Thermal analysis combined with microstructural and EDX analysis was used to determine the phase transformation temperatures during solidification process. Experimental results show that when the Al content is below 4 wt%, a peritectic reaction, L + Al2Y → α-Mg, occurs after the intermetallic Al2Y forms directly from the melt as a pro-peritectic phase. Once the Al content is above 4 wt%, an eutectic reaction occurs at a lower temperature. The presence of the pro-peritectic phase can lead to nucleation of α-Mg directly through a peritectic reaction although grain refining efficiency is also closely related to the active particle size. In the case where solidification does not involve a peritectic reaction, the growth restriction factor, quantitatively the Q-value, governs the grain refining efficiency. Higher Q-value corresponds to finer grains.

Grain refinement of Mg–Al alloys by optimization of process parameters based on three-dimensional finite element modeling of roll casting

To study the influence of roll casting process parameters on temperature and thermal-stress fields for the AZ31 magnesium alloy sheets, three-dimensional geometric and 3D finite element models for roll casting were established based on the symmetry of roll casting by ANSYS software. Meshing method and smart-sizing algorithm were used to divide finite element mesh in ANSYS software. A series of researches on the temperature and stress distributions during solidification process with different process parameters were done by 3D finite element method. The temperatures of both the liquid–solid two-phase zone and liquid phase zone were elevated with increasing pouring temperature. With the heat transfer coefficient increasing, the two-phase region for liquid–solid becomes smaller. With the pouring temperature increasing and the increase of casting speed, the length of two-phase zone rises. The optimized of process parameters (casting speed 2 m/min, pouring temperature 640 °C and heat transfer coefficient 15 kW/(m2·°C) with the water pouring at roller exit was used to produce magnesium alloy AZ31 sheet, and equiaxed grains with the average grain size of 50 μm were achieved after roll casting. The simulation results give better understanding of the temperature variation in phase transformation zone and the formation mechanism of hot cracks in plates during roll casting and help to design the optimized process parameters of roll casting for Mg alloy.

Poisoning-free effect of calcium on grain refinement of Mg–3%Al alloy containing trace Fe by carbon inoculation

Mg-3%Al alloy was modified by combining Ca addition with carbon inoculation. The effects of Fe addition and addition sequence on the grain refinement were investigated. A higher grain refining efficiency could be obtained for the Mg–Al alloy modified by combining Ca addition with carbon inoculation. Fe addition and addition sequence had no obvious effect on the grain refinement. Ca addition could effectively avoid grain-coarsening resulting from Fe in the carbon-inoculated Mg–Al alloy. The Al-C-O particles, actually being Al4C3, should act as potent substrates for α-Mg grains in the sample treated by combining Ca addition with carbon inoculation. However, the duplex-phase particles of Al4C3 coated on Al-Fe or Al-C-Fe should be the potent substrates for α-Mg grains if Fe existed in the Mg–Al melt. Ca addition can contribute to the formation of the particles of Al4C3 coated on Al-Fe or Al-C-Fe, regardless of the Fe addition sequence. The poisoning effect of Fe was effectively inhibited in the carbon-inoculated of Mg-Al alloy due to Ca addition, namely, Ca has a poisoning-free effect.

Influence of Al4C3 Particles on Grain Refinement of Mg–3Al Alloys

Al–Si/Al4C3 master alloy has been developed by reacting the SiC particles in Al melt. The extent of SiC conversion to Al4C3 in the Al–Si/Al4C3 master alloy has been calculated using optical emission spectroscopy. Experimental results indicated that only 70 % of SiC particles have been converted into Al4C3 after the reaction between Al and SiC in Al/5 wt% SiCp composites at 900 °C. The grain refining efficiency of Al–Si/Al4C3 master alloy has been assessed by adding this into the Mg–3Al alloy. Grain size of Mg–3Al alloy has been significantly refined from 480 to 220 μm by the addition of 0.07 wt% of Al4C3 particles in the form of Al–Si/Al4C3 master alloy.

Grain refinement of Mg–10Gd alloy by Al additions

Abstract

Mechanisms of grain refinement in Mg–6Al–1Zn alloy during hot deformation

Abstract Mechanisms of grain refinement were investigated in an extruded Mg–6Al–1Zn alloy during hot compression at 623 K and a true strain rate of 3 × 10−3 s−1. With increasing strain, grain fragmentation gradually took place; the dominant grain refinement mechanism, however, depended on the strain. At strains up to ɛ = 0.1, mechanical twinning contributed notably to grain refinement and to the formation of high angle boundaries. At medium to high strains, continuous dynamic recrystallization took place. Kinking contributed to grain fragmentation at all strains. The latter two mechanisms also increased the fraction of low to medium angle boundaries.

Mechanism of grain refinement of Mg–Al alloys by SiC inoculation

The mechanism of grain refinement was investigated for Mg–Al alloys inoculated with SiC particles. Contrary to the previously reported Al4C3 hypothesis, the ternary carbide Al2MgC2 was observed, which has a crystal structure closer to that of Mg than to that of Al4C3. In the centre of the grains, one or more “hillocks” enriched in Al and C were observed. Based on the observed phenomena, a novel mechanism is suggested to explain the grain refinement of Mg–Al alloys with the addition of SiC particles.

Microstructural refinement and tensile properties enhancement of Mg–3Al alloy using charcoal additions

Significant grain refinement in Mg–3Al alloy is achieved with the addition of charcoal due to the formation of Al4C3 particles, which act as effective nuclei for magnesium grains. Addition of 0.5 wt% charcoal has lead to reduced grain size of Mg–3Al alloy from 500 to 80m and no substantial grain refinement is obtained on further addition of charcoal. The results further reveal that the prolonged holding of the melt after the addition of charcoal has not affected the grain refining efficiency of Al4C3. Steady increase in tensile properties observed with increasing amount of charcoal addition has been attributed to the grain refinement and the presence of fine Al4C3 particles. The strengthening mechanisms due to charcoal addition are discussed in terms of Hall–Petch relation and dispersion strengthening. The predicted values are in good agreement with experimental results. © 2010 Elsevier B.V. All rights reserved.

Effects of Fe addition and addition sequence on carbon inoculation of Mg–3%Al alloy

The Mg–3%Al melt was treated by carbon inoculation and/or Fe addition. The effects of Fe addition and addition sequence on the carbon inoculation of Mg–3%Al alloy were investigated in the present study. The role of Fe in the grain refinement of Mg–3%Al alloy treated by carbon inoculation was closely associated with the operating sequence of carbon inoculation and Fe addition. Fe has no obvious effect on the grain refinement of Mg–3%Al alloy by carbon inoculation under the condition that Fe pre-existed in the Mg–3%Al melt before carbon inoculation. However, Fe played an inhibiting role under the condition that the Mg–3%Al melt had been inoculated by carbon before Fe addition. The Al–C–O particles were observed in the sample treated only by carbon inoculation. In addition to Al–C–O particles, Al–C–O–Fe particles could be observed in the sample treated by Fe addition and then carbon inoculation. These Al–C–O and Al–C–O–Fe particles, actually being Al–C and Al–C–Fe phases, should be the potent nucleating substrates for Mg grains, resulting in the grain refinement. However, the Al–C–O–Fe-rich intermetallic particles were mainly observed in the samples treated by carbon inoculation and then Fe addition. The Al–C–O–Fe particles, actually being Al–C–Fe phases, formed under this condition should not be the potent nucleating substrates for Mg grains, resulting in the grain coarsening.

Grain refining mechanisms in Mg–Al alloys with Al 4C 3 microparticles

Experiments were conducted to examine the grain refining mechanisms in AM60B, pure Mg, and Mg–6%Al with the addition of 5 wt% aluminum carbide (Al 4C 3). Grain refinement was observed in the AM60B and pure Mg with the addition of 5 wt% Al 4C 3 via two different mechanisms respectively, i.e. duplex nucleation hypothesis (Al 4C 3 → Al 8Mn 5 → α-Mg) in AM60B and Al 4C 3 nuclei hypothesis (Al 4C 3 → α-Mg) in pure Mg. It is suggested that Mn is required to facilitate significant grain refinement in Mg–Al alloys containing ≥6% Al due to the segregating behavior of Al 4C 3 particles to the solid–liquid (S–L) interface. Mechanical properties (yield strength, tensile strength, ductility, and microhardness) were enhanced by the addition of Al 4C 3 to AM60B alloy.

Grain refining efficiency of a new Al–1B–0.6C master alloy on AZ63 magnesium alloy

A new Al–1B–0.6C master alloy for grain refinement of Mg–Al-based alloys has been fabricated by melt reaction in the present work. Through XRD and EPMA detection, it is found that Al–1B–0.6C master alloy mainly contains Al3BC particles with the size distribution from 2 μm to 8 μm. The reaction between Al4C3 and B in Al melt forms the new Al3BC phase. Grain refinement experiments reveal that the master alloy can refine AZ63 (Mg–6Al–3Zn–0.4Mn) alloy efficiently. At 760 °C, the grain size is sharply reduced from 710 μm to 70 μm with the addition of 2 wt.% Al–1B–0.6C master alloy, and the grain morphology of α-Mg transits from a characteristic sixfold symmetrical shape to a petal-like shape. The grain refining mechanism is attributed to the presence of Al3BC particles in the master alloy which can act as effective nucleating substrates of primary α-Mg.

Grain refinement of Mg–Al cast alloy by the addition of manganese carbonate

Abstract The effect of MnCO3 addition on grain refinement of Mg–Al alloys was investigated. The microstructural changes induced by MnCO3 addition indicate that it has excellent grain refining efficiency for Mg–9 wt.%Al alloy. In addition the average grain size was reduced from 480 to 61 μm by 0.6 wt.% addition. This is attributed to inoculation of MnCO3, which brings about the formation of potent heterogeneous nucleants such as MgO, Al4C3, and Al8Mn5 before solidification of α-Mg as well as melt agitation by the release of CO2 gas.

Different elements-induced destabilisation of TiC and its application on the grain refinement of Mg–Al alloys

The destabilisation of TiC and its application on the grain refinement of Mg–Al alloys is studied by the experiment and CASTEP calculation. Al 4C 3-containing refiners for Mg–Al based alloys are easily prepared in the liquid Al–Ti–C–Si alloy, but the TiAl x Si y formed simultaneously will poison the refining efficiency of Al 4C 3. In contrast to Si, B element can improve the stabilization of TiC in the Al melt; however, the addition of B is essential in Al 4C 3-containing refiners prepared by the destabilisation of TiC in order to transfer the Ti into TiB 2 particles. In this case, the poisoning effect of Ti can be avoided and the formed Al 4C 3 can be fully worked as the substrates for α-Mg.

Microstructure and mechanical properties of Mg96Zn2Y2 alloy prepared by extrusion of machined chips

Hot extrusion has been carried out at 623 K on machined chips of Mg96Zn2Y2 (at%) alloy. Microstructure and mechanical properties of the extruded Mg96Zn2Y2 alloy have been investigated. The extruded Mg96Zn2Y2 alloy was composed of α-Mg, Mg12ZnY and Mg3Zn3Y2 phases, and the Mg grain had a mean grain size of 450 nm. The Mg12ZnY phase was frequently observed inside the fine Mg grains. Additionally, oxidation was occurred around cavities remained after extrusion. The extruded alloy exhibited a high 0.2% proof strength of 495 MPa and elongation of failure to 3% at room temperature. Grain refinement of Mg and dispersion of Mg12ZnY and Mg3Zn3Y2 phases caused by hot extrusion lead to high strength at room temperature. Furthermore, the alloy extrusion also exhibited the superplasticity at temperatures of 623 K and 723 K with initial strain rates from 2×10−1 s−1 to 2×10−3 s−1. And also the maximum elongation was 450% at 723 K with initial strain rate of 2×10−3 s−1. The grain boundary sliding of Mg grains is dominant deformation mechanism for the alloy at high temperature ranges.

Grain refinement of Mg–Al based alloys by a new Al–C master alloy

A new Al–C master alloy for grain refinement on Mg–Al based alloys has been fabricated by powder metallurgy. Al4C3 is formed by reaction between part of f.c.c Al(C) solid solution and aluminum during fabrication, and the net-like mixture of Al4C3 and Al(C) solid solution is located at the boundaries of aluminum particles. Milling and pressing of graphite and aluminum powders change the nature of graphite and ensure the kinetics conditions of the reaction between the two phases. Grain refinement experiment shows Al–1C master alloy can efficiently refine AZ31 (Mg–3%Al–1%Zn). At 760 °C, when adding 2 wt.% Al–1C master alloy, the grain size is reduced sharply from 400 μm to 140 μm comparing to the sample added 2 wt.% commercial pure aluminum, and the grain morphology of α-Mg transits from a characteristic sixfold symmetrical shape to a petal-like shape.

Effect of melt superheating treatment on the cast microstructure of Mg–1.5Si–1Zn alloy

The effect of melt superheating treatment on the microstructure of Mg–1.5Si–1Zn alloy is investigated in this article. The microstructure of samples poured into sand and metal molds shows that the primary Mg2Si is considerably refined in size when the melt is superheated from 750 to 900 °C. However, its polyhedral morphology does not change. In addition, also the size of eutectic Mg2Si phase obviously decreases, but the morphology still exhibits Chinese script type. Meanwhile, it is concluded that the reduction of the heredity plays an important role in the grain refinement of Mg–1.5Si–1Zn alloy.

A New Analytical Approach to Reveal the Mechanisms of Grain Refinement

AbstractThis paper presents an overview of a new methodology for investigating the grain refinement performance of alloys and master alloys and then uses this methodology to shed new light on the mechanisms occurring during superheating and native grain refinement, and the effect of iron and manganese on grain refinement in magnesium alloys. The methodology also describes changes in grain size upon Zr grain refinement of Mg and has been used to analyse the potential for the use of SiC to grain refine Mg‐Al alloys. With this new methodology, and the knowledge it generates, the potential for the discovery of new or improved refiners is significantly enhanced.

Grain refining mechanism in Mg–Al base alloys with carbon addition

In this study, carbon addition affects the formation mechanism and morphology of Al8(Mn, Fe)5, which serves as a nucleation site for α-Mg, conclusively leading to grain refinement of Mn-containing Mg–Al alloys. However, the grain size was decreased on slightly by carbon addition in Mn-free Mg–Al alloys, where Al4C3 particles were observed in the eutectic region. Therefore, it is suggested that Mn is necessary for considerable grain refinement of Mg–Al alloys, and that Al8(Mn, Fe)5 is an effective nucleant in Mn-containing Mg–Al alloys.

Grain refinement of Mg–Al(–Mn) alloys by SiC additions

The addition of SiC particles effectively grain refined a range of Mg-Al alloys. The greatest reductions in grain size were found for the alloys with lower Al contents. The presence of Mg2Si in the microstructure after that SiC addition, and consideration of phase equilibria suggested that the SiC transforms to Al4C3, and this is the actual nucleant. The addition of Mn poisoned the grain refining effect of the SiC addition, probably due to the formation of less potent Al-Mn-carbides. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of manganese on grain refinement of Mg–Al based alloys

Manganese is a grain refiner for high purity Mg-3%Al, Mg-6%Al, Mg-9%Al, and commercial AZ31 (Mg-3%Al-1%Zn) alloys when introduced in the form of an Al-60%Mn master alloy splatter but the use of pure Mn flakes and ALTAB (TM) Mn75 tablets shows no grain refinement. Long time holding of the melt at 730 degrees C leads to an increase in grain size. The mechanism is attributed to the presence of all epsilon-AlMn phase (hexagonal close-packed) in the master alloy splatter. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.