scholarly journals Effect of grain refinement on the microstructure, dendrite coherency and porosity of AZ91E magnesium alloy

2021 ◽  
Author(s):  
Mihai Vlasceanu
Keyword(s):  
Magnesium Alloy ◽  
Grain Refinement ◽  
Growth Mechanism ◽  
Solid Fraction ◽  
Dendrite Growth ◽  
Dendritic Morphology ◽  
Al Alloys ◽  
Mg Alloys ◽  
Grain Refiner ◽  
Dendrite Coherency

Magnesium (Mg) alloys present a promising alternative to aluminum (Al) alloys in lightweight applications. However, relative to Al alloys, Mg alloys have poor castability. Castability is influenced significantly by the dendrite coherency point (DCP), which represents the temperature, time, and solid fraction at which an interlocking solid network forms during solidification. An increase in the solid fraction at coherency may improve the castability of the alloy and reduce casting defects such as porosity, hot tears and misruns. A successful method for increasing the solid fraction at the DCP in Al alloys involves the use of grain refiners such as titanium (Ti). However, the influence of Ti refiners on the DCP in Mg alloys has not been thoroughly investigated. The objective of this research was to study the effect of Al-5Ti-1B refiner on the dendrite growth mechanism, DCP and porosity of AZ91E magnesium alloy. This thesis is a pioneering effort in relating the grain refinement effect of Ti on the DCP, coherency solid fraction, and porosity development during the solidification of Mg alloy, AZ91E. It represents an important step in improving the castability of Mg alloys. Varying levels of Al-5Ti1B grain refiner (0.005, 0.05, 0.1, 0.2, and 0.3 wt.% Ti) were added to AZ91E. The effect of Al-5Ti-1B grain refiner on the microstructure and dendrite growth mechanism of AZ91E was investigated. Quench experiments were performed to observe transformations in the dendritic morphology that resulted from the refiner additions. The growth rate and DCP were determined using the rheological method. The changes in porosity levels were determined for the grain refiner additions.

scholarly journals Effect of grain refinement on the microstructure, dendrite coherency and porosity of AZ91E magnesium alloy

2021 ◽  
Author(s):  
Mihai Vlasceanu
Keyword(s):  
Magnesium Alloy ◽  
Grain Refinement ◽  
Growth Mechanism ◽  
Solid Fraction ◽  
Dendrite Growth ◽  
Dendritic Morphology ◽  
Al Alloys ◽  
Mg Alloys ◽  
Grain Refiner ◽  
Dendrite Coherency

Magnesium (Mg) alloys present a promising alternative to aluminum (Al) alloys in lightweight applications. However, relative to Al alloys, Mg alloys have poor castability. Castability is influenced significantly by the dendrite coherency point (DCP), which represents the temperature, time, and solid fraction at which an interlocking solid network forms during solidification. An increase in the solid fraction at coherency may improve the castability of the alloy and reduce casting defects such as porosity, hot tears and misruns. A successful method for increasing the solid fraction at the DCP in Al alloys involves the use of grain refiners such as titanium (Ti). However, the influence of Ti refiners on the DCP in Mg alloys has not been thoroughly investigated. The objective of this research was to study the effect of Al-5Ti-1B refiner on the dendrite growth mechanism, DCP and porosity of AZ91E magnesium alloy. This thesis is a pioneering effort in relating the grain refinement effect of Ti on the DCP, coherency solid fraction, and porosity development during the solidification of Mg alloy, AZ91E. It represents an important step in improving the castability of Mg alloys. Varying levels of Al-5Ti1B grain refiner (0.005, 0.05, 0.1, 0.2, and 0.3 wt.% Ti) were added to AZ91E. The effect of Al-5Ti-1B grain refiner on the microstructure and dendrite growth mechanism of AZ91E was investigated. Quench experiments were performed to observe transformations in the dendritic morphology that resulted from the refiner additions. The growth rate and DCP were determined using the rheological method. The changes in porosity levels were determined for the grain refiner additions.

Rheological Transitions at Low Solid Fraction in Solidifying Magnesium Alloy AZ91

2007 ◽  
Vol 561-565 ◽  
pp. 1067-1070 ◽  
Author(s):  
Christopher M. Gourlay ◽  
B. Meylan ◽  
Arne K. Dahle
Keyword(s):  
Grain Size ◽  
Magnesium Alloy ◽  
Mechanical Behaviour ◽  
Defect Formation ◽  
Dendritic Morphology ◽  
Al Alloys ◽  
Dendritic Solidification ◽  
Alloy Az91 ◽  
Magnesium Alloy Az91 ◽  
Dendrite Coherency

Transitions in the mechanical behaviour of solidifying alloys influence feeding mechanisms and defect formation during many casting processes. This paper explores dendrite coherency and the cracking transition during the equiaxed dendritic solidification of Mg alloy AZ91 using the continuous-torque technique and vane rheometry. The two techniques yielded similar dendrite coherency values of ~17% solid, and the cracking transition occurred at 40% solid in vane rheometry tests. These transition values are similar to those reported for Al alloys with equiaxed dendritic morphology and a similar grain size.

scholarly journals Grain Refinement of AZ91 Magnesium Alloy Induced by Al-V-B Master Alloy

Metals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1333 ◽  
Author(s):  
Wang Chang ◽  
Yanping Shen ◽  
Yueying Su ◽  
Long Zhao ◽  
Yunhu Zhang ◽  
...  
Keyword(s):  
Magnesium Alloy ◽  
Comparative Study ◽  
Grain Refinement ◽  
Master Alloy ◽  
Al Alloys ◽  
Az91 Alloy ◽  
Grain Refiner ◽  
Az91 Magnesium Alloy ◽  
Master Alloys ◽  
Az91 Magnesium

It has long been recognized that grain refinement of Mg-Al alloys is difficult, although various methods have been tried. In the present paper, a novel grain refiner, Al-3.4V-1B master alloy, has been developed to refine the as-cast AZ91 alloy. A comparative study on grain refinement effects of Al-3.4V-1B, Al-5V, and Al-3Ti-1B master alloys was performed under the same solidification conditions. It is shown that Al-3.4V-1B master alloy not only has significant grain refinement ability, but also keeps stable anti-fading capacity with holding time up to 2 h. Based on the analysis of grain refinement, VB2 particles introduced by Al-3.4V-1B master alloy are the heterogeneous nuclei for AZ91 alloy.

scholarly journals Novel grain refinement of AZ91E magnesium alloy and the effect on hot tearing during solidfication

2021 ◽  
Author(s):  
Abdallah Elsayed
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Grain Refinement ◽  
Magnesium Alloys ◽  
Hot Tearing ◽  
Grain Refining ◽  
Grain Refiner ◽  
Structural Applications ◽  
Hot Tearing Susceptibility

For the A1-5Ti-1B grain refiner, the addition of 0.1 wt.% provided a 68 % reduction in grain size as compared to the unrefined AZ91E alloy at a holding time of five minutes. Grain growth restriction by TiB₂ particles was the source of grain refinement. With the addition of A1-5Ti-1B, only a small reduction in hot tearing susceptibility ws observed because large TiA1₃ particles bonded poorly with the eutectic and blocked feeding channels.The addition of 1.0 wt.% A1-1Ti-3B provided a grain size reduction of 63% as compared to the unrefined AZ91E alloy at a holding time of five minutes. The grain refinement with A1-1Ti-3B addition was attributed to a combination of TiB₂ grain growth restriction and A1B₂ nucleating sites. A significant reduction in hot tearing susceptibility was observed with A1-1Ti-3B addition as a result of a higher cooling rate and shorter local soldification time as compared to the AZ91E alloy. The reduction in hot tearing susceptibility was attributed to the good interface between eutectic and TiB₂ particles. Both grain refiners demonstrated a good resistance to fading during the holding times investigated. In addition, the AZ91E + A1-5Ti-1B and AZ91E + A1-1Ti-3B castings showed much fewer dislocation networks as compared to the untreated AZ91E casting.The development of efficient A1-Ti-B refiners can also improve castability of magnesium alloys. In addition, the fade resistant A1-Ti-B grain refiners can reduce operating costs and maintain productivity on the foundry floor. Thus, magnesium alloy with A1-Ti-B treatment have the potential for more demanding structural applications in the automobile and aerospace industries. Vehicle weight in the aerospace and automotive industries directly impacts carbon emissions and fuel efficiency. An increase in the use of lightweight materials for structural applications will result in lighter vehicles. Low density materials, such as magnesium (1.74 g/cm³) are a potential alternative to aluminium (2.70 g/cm³), to reduce component weight in structural applications.However, current magnesium alloys still do not have adequate mechanical properties and castability to meet the performance specifications of the automotive and aerospace industries. Grain refinement can significantly improve mechanical properties and reduce hot tearing during permanent mould casting. Recently, Al-Ti-B based grain refiners have shown potential in grain refining magnesium-aluminum alloys such as AZ91E. This study investigates the grain refining efficiency and fading of A1-5Ti-1B and A1-1Ti-3B in AZ91E magnesium alloy and their subsequent effect on hot tearing.The grain refiners were added at 0.1, 0.2, 0.5 and 1.0 wt.% levels. For the grain refinement and fading experiments, the castings were prepared using graphite moulds with holding times of 5, 10 and 20 minutes. For the hot tearing experiments, castings were produced representing the optimal addition level of each grain refiner. The castings were prepared using a permanent mould with pouring and mould temperatures of 720 and 180 ºC, respectively. The castings were characterized using SEM, TEM, optical microscopy and thermal analysis.

Effects of Melt Treatment on Dendrite Coherency of A357 Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 3886-3890
Author(s):  
Zhong Wei Chen ◽  
Pei Chen ◽  
Li Fan
Keyword(s):  
Thermal Analysis ◽  
Growth Rate ◽  
Cooling Rate ◽  
Solid Fraction ◽  
Dendrite Growth ◽  
A357 Alloy ◽  
Dendrite Coherency Point ◽  
Melt Treatment ◽  
Coherency Point ◽  
Dendrite Coherency

The Dendrite Coherency Point (DCP) of A357 alloy was determined after different melt treatments by double thermocouples, and the coherency solid fraction (fscoh) was calculated by thermal analysis. The results of dendrite coherency properties show that fscoh values increase with increased cooling rate for A357 alloy. For A357 alloys, fscoh values increase after grain refined and melt superheat treatment. The coherency point was found to be dependent on not only the morphology of the dendrites but also the dendrite growth rate.

Theoretical and Practical Considerations of Grain Refinement of Mg-Al Alloys

2005 ◽  
Vol 488-489 ◽  
pp. 299-302 ◽  
Author(s):  
L. Lu ◽  
Arne K. Dahle ◽  
John A. Taylor ◽  
David H. StJohn
Keyword(s):  
Grain Refinement ◽  
Magnesium Alloys ◽  
Al Alloys ◽  
Experimental Results ◽  
Grain Refiner ◽  
Carbon Based

The fundamentals of grain refinement are reviewed with particular focus on magnesium alloys. This is followed by considerations of the theoretical and practical aspects of grain refinement of Mg-Al alloys by carbon-based grain refiners. Finally, experimental results using Al4C3 as a potential grain refiner are presented and discussed.

ULTRA FINE-GRAINED AZ31 MAGNESIUM ALLOY OBTAINED BY A COMBINATION OF GRAIN REFINEMENT AND EQUAL CHANNEL ANGULAR PRESSING

2012 ◽  
Vol 05 ◽  
pp. 307-315 ◽  
Author(s):  
S.A. TORBATI-SARRAF ◽  
R. MAHMUDI
Keyword(s):  
Grain Size ◽  
Magnesium Alloy ◽  
Grain Refinement ◽  
Grain Growth ◽  
Equal Channel Angular Pressing ◽  
Boundary Migration ◽  
Grain Refiner ◽  
Fine Grained ◽  
Angular Pressing ◽  
Grain Size Distributions

Different amounts of Al -5 Ti -1 B master alloy ( TiBAl ) were added to the AZ 31 magnesium alloy ( Mg -3 Al -1 Zn -0.2 Mn ) as grain refiner and the resulting microstructure and grain size distributions were studied after extrusion and equal channel angular pressing (ECAP). Results showed that the addition of 0.6% TiBAl had the strongest grain refinement effect, reducing the grain sizes by 54.5 and 48.5% in the extruded and ECAPed conditions, respectively. The observed grain refinement was partly due to the presence of the thermally-stable micron- and submicron-sized particles in the melt which act as nucleation sites during solidification. During the high-temperature extrusion and ECAP processes, dynamic recrystallization (DRX) and grain growth are likely to occur. However, the mentioned particles will help in reducing the grain size by the particle stimulated nucleation (PSN) mechanism. Furthermore, the pinning effect of these particles can oppose grain growth by reducing the grain boundary migration. These two phenomena together with the partitioning of the grains imposed by the severe plastic deformation in the ECAP process have all contributed to the achieved ultrafine-grained structure in the AZ 31 alloy.

Influence of a Novel Master Alloy Addition on the Grain Refinement of Al-Si Cast Alloys

2013 ◽  
Vol 765 ◽  
pp. 311-315 ◽  
Author(s):  
Leandro Bolzoni ◽  
Magdalena Nowak ◽  
N. Hari Babu
Keyword(s):  
Grain Refinement ◽  
Master Alloy ◽  
Intermetallic Phases ◽  
Al Alloys ◽  
Grain Structure ◽  
Grain Refiner ◽  
Casting Alloys ◽  
Alloy Addition ◽  
Cast Alloys ◽  
The Impact

The grain refinement practice using Ti based chemical additions is well established for wrought Al alloys, especially in the last few decades. In the case of Al-Si casting alloys the practice of adding grain refiners and the impact on castability is not well established in industries. The main reason is the chemical instability of conventionally known Ti based grain refiner which reacts with silicon forming intermetallic phases. Recently, researchers at Brunel University have identified a novel chemical composition that can refine the grain structure of Al-Si alloys in an effective way. Over the last year, this novel grain refiner in the form of master alloy was developed and tested in various Al-Si cast alloys that are commonly used in industry. Significant grain refinement is obtained when the master alloy is added to the liquid metal prior to casting. Moreover, the grain size of the Al-Si cast alloys is observed to be less sensitive to cooling rate when the master alloy is added. In this work, the influence of addition of the master alloy on microstructural evolution of various Al-Si alloys cast under various cooling rates is presented.

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