scholarly journals A study on grain refinement of AZ91E magnesium alloy with Al-5TiB₂, AI-Al₄C₃ and ZnO additions

2021 ◽  
Author(s):  
Kenneth Lee
Keyword(s):  
Grain Refinement ◽  
Base Alloy ◽  
Hot Tearing ◽  
Mg Alloys ◽  
Grain Refiner ◽  
Dendritic Microstructure ◽  
Refinement Efficiency ◽  
Average Grain Size ◽  
Refinement Mechanism ◽  
Environmentally Safe

There is great interest in increasing the use of magnesium (Mg) alloys in transportation applications to reduce weight. The use of these alloys would increase if their strength and castability were improved. Through grain refinement, it is possible to achieve significant improvement in specific mechanical properties such as strength and hardness. For aluminum (A1)-containing Mg alloys, a commonly used grain refiner is hexachloroethane (C₂Cl₆). Though effective, C₂Cl₆ use releases harmful chlorinated hydrocarbons. It is therefore desired to find novel grain refiners that are effective and environmentally safe. This thesis focused on the grain refinement of AZ9lE alloy with three refiners: Al-5TiB₂, Al-A1₄C₃ and ZnO. The refiners were chosen due to their known grain refinement efficiency in low-Al Mg or Mg-Zn alloys. Castings with each refiner were made in graphite molds to establish i) the optimum addition levels to achieve the smallest average grain size and ii) the effect of holding time on fading of grain refinement efficiency. These castings ere used to collect thermal data and sectioned for microscopy and hardness testing. Castings were also made with the optimum parameters in a permanent mold specifically designed to investigate hot tearing susceptibility. The results indicated that all three additions enabled grain refinement of the base alloy, and no fading of grain refiner efficiency was observed. These refiners transformed the coarse dendritic microstructure in AZ9lE to one that was equiaxed and globular. At optimal levels, the refinement mechanism was heterogeneous nucleation. Also, hot tearing was significantly decreased with all refiners except for ZnO. The excess Zn from ZnO addition led to an increase in the freezing range, thus increasing the hot tear severity. The hardness of AZ9lE did not increase with ZnO addition as it did with the other two refiners.

scholarly journals A study on grain refinement of AZ91E magnesium alloy with Al-5TiB₂, AI-Al₄C₃ and ZnO additions

2021 ◽  
Author(s):  
Kenneth Lee
Keyword(s):  
Grain Refinement ◽  
Base Alloy ◽  
Hot Tearing ◽  
Mg Alloys ◽  
Grain Refiner ◽  
Dendritic Microstructure ◽  
Refinement Efficiency ◽  
Average Grain Size ◽  
Refinement Mechanism ◽  
Environmentally Safe

There is great interest in increasing the use of magnesium (Mg) alloys in transportation applications to reduce weight. The use of these alloys would increase if their strength and castability were improved. Through grain refinement, it is possible to achieve significant improvement in specific mechanical properties such as strength and hardness. For aluminum (A1)-containing Mg alloys, a commonly used grain refiner is hexachloroethane (C₂Cl₆). Though effective, C₂Cl₆ use releases harmful chlorinated hydrocarbons. It is therefore desired to find novel grain refiners that are effective and environmentally safe. This thesis focused on the grain refinement of AZ9lE alloy with three refiners: Al-5TiB₂, Al-A1₄C₃ and ZnO. The refiners were chosen due to their known grain refinement efficiency in low-Al Mg or Mg-Zn alloys. Castings with each refiner were made in graphite molds to establish i) the optimum addition levels to achieve the smallest average grain size and ii) the effect of holding time on fading of grain refinement efficiency. These castings ere used to collect thermal data and sectioned for microscopy and hardness testing. Castings were also made with the optimum parameters in a permanent mold specifically designed to investigate hot tearing susceptibility. The results indicated that all three additions enabled grain refinement of the base alloy, and no fading of grain refiner efficiency was observed. These refiners transformed the coarse dendritic microstructure in AZ9lE to one that was equiaxed and globular. At optimal levels, the refinement mechanism was heterogeneous nucleation. Also, hot tearing was significantly decreased with all refiners except for ZnO. The excess Zn from ZnO addition led to an increase in the freezing range, thus increasing the hot tear severity. The hardness of AZ9lE did not increase with ZnO addition as it did with the other two refiners.

scholarly journals The Interactions Between Oxide Film Inclusions and Inoculation Particles TiB2 in Aluminum Melt

2021 ◽  
Author(s):  
Jiawei Yang ◽  
Sarina Bao ◽  
Shahid Akhtar ◽  
Yanjun Li
Keyword(s):  
Grain Refinement ◽  
Master Alloy ◽  
Large Fraction ◽  
Oxide Films ◽  
Grain Refiner ◽  
Particle Sedimentation ◽  
Aluminum Melt ◽  
Refinement Efficiency ◽  
Long Time ◽  
Commercial Purity Aluminum

AbstractIn this work, a systematic study on the interactions between aluminum oxide films and TiB2 grain refiner particles and their effect on grain refinement behavior have been conducted. Oxide films were introduced into a commercial purity aluminum melt by adding AA 6061 alloy chips while the grain refiner particles were introduced by adding Al-3T-1B master alloy. Strong sedimentation of TiB2 grain refiner particles was observed in aluminum melt without chip addition during long-time settling. Most of the TiB2 particles were settled and accumulated at the bottom of crucible. In contrast, the sedimentation of TiB2 particles is much less in the melt with the addition of oxide films. A large fraction of TiB2 particles were found to be adhered to the oxide films located at the top part of the crucible, which inhibited the sedimentation of grain refiner particles. TP-1 type tests were also done to study the grain refinement efficiency of Al-3Ti-1B master alloy under different melt cleanliness and settling time. It is found that sedimentation of TiB2 particles greatly reduces the grain refinement efficiency. The introduction of oxide films seems to slightly alleviate the fading effect. This is owing to the strong adherence between the oxide films and TiB2 particles, which leads to a retardation of particle sedimentation.

Grain Refinement and Hot Tearing of Aluminium Alloys - How to Optimise and Minimise

2009 ◽  
Vol 630 ◽  
pp. 213-221 ◽  
Author(s):  
Mark Easton ◽  
David H. StJohn ◽  
Lisa Sweet
Keyword(s):  
Grain Refinement ◽  
Aluminium Alloys ◽  
Hot Tearing ◽  
Key Factors ◽  
Grain Refiner ◽  
Factors Affecting ◽  
Equiaxed Grains

Grain refinement and hot tearing are important key factors affecting the quality of castings. There have been substantial advances in the understanding of both of these phenomena over the last two decades. The paper discusses strategies for obtaining the lowest cost grain refiner addition and provides an explanation for how the refinement of equiaxed grains leads to a reduction in hot tear susceptibility. However, it also provides a warning that adding more grain refiner may not be better for reducing hot tear susceptibility. Alloy factors affecting hot tearing are also discussed. Finally, a list of six key considerations is provided to help casthouse and foundry engineers when trying to optimise grain refinement and reduce hot tearing.

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.

Application of High-Pressure Sliding for Grain Refinement of Al and Mg Alloys

2010 ◽  
Vol 667-669 ◽  
pp. 91-96 ◽  
Author(s):  
Kiyonari Tazoe ◽  
Shuji Honda ◽  
Z. Horita
Keyword(s):  
High Pressure ◽  
Strain Rate ◽  
Grain Refinement ◽  
High Pressure Torsion ◽  
Initial Strain Rate ◽  
Mg Alloys ◽  
Initial Strain ◽  
Mg Alloy ◽  
Al Alloy ◽  
Average Grain Size

An earlier study showed that high-pressure sliding (HPS) is effective for grain refinement of pure Al in a rectangular sheet form using the principle of high-pressure torsion. In this study, the HPS is applied for grain refinement of an Al-3%Mg-0.2%Sc alloy and an AZ61 Mg alloy. HPS was conducted under a pressure of 1 GPa with sliding distances of 10 to 30 mm at room temperature for the Al alloy and at 473 K for the Mg alloy The average grain size is ~300 nm for both the Al and Mg alloys, respectively. Tensile tests showed that a superplastic elongation of ~1500% is achieved in the Al-3%Mg-0.2%Sc alloy at 573 K with an initial strain rate of 3.3x10-3 s-1 and of ~600% in the AZ61 alloy at 573 K with an initial strain rate of 1x10-3 s-1.

scholarly journals Effect of Inclusion and Filtration on Grain Refinement Efficiency of Aluminum Alloy

2022 ◽  
Author(s):  
Jiawei Yang ◽  
Yijiang Xu ◽  
Sarina Bao ◽  
Shahid Akhtar ◽  
Ulf Tundal ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Refinement ◽  
Oxide Films ◽  
Pilot Scale ◽  
Ceramic Foam ◽  
Grain Refiner ◽  
Aluminum Melt ◽  
Refinement Efficiency ◽  
Master Alloys ◽  
And Performance

AbstractIt is well known that the filtration efficiency of ceramic foam filters (CFF) on aluminum melt can be significantly reduced by the addition of grain refiner particles under a high inclusion load. Also, it is usually considered that the filtration process has little impact on grain refinement efficiency. In this work, the influence of inclusions and filtration on the grain refinement effect of AA 6060 alloy has been studied. This was done through TP-1 type solidification experiments where the aluminum melt prior to and after the filter during a pilot-scale filtration test was investigated. In the experiments, 80 PPi CFFs were used to filtrate aluminum melt with an ultra-high inclusion load and two addition levels of Al–3Ti–1B master alloys. It is found that both inclusions and filtration significantly reduce the grain refinement efficiency of the grain refiner master alloys. A detailed characterization of the used filters shows that the reduction of grain refinement efficiency is due to the strong adherence of TiB2 particles to the oxide films, which are blocked by the CFF during filtration. A grain size prediction model based on deterministic nucleation mechanisms and dendritic growth kinetics has been applied to calculate the solidification grain size and estimate the loss of effective grain refiner particles during filtration. It is shown that due to the strong adherence between TiB2 particles and oxide films in the melt, the high addition level of aluminum chips also has an influence on reducing the grain refinement efficiency of aluminum melt without filtration. The results of this study extended our understanding of the behavior and performance of inoculant particles in CFF and their interactions with the inclusions.

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 A study of grain refinement of AZ91E and Mg-9 wt.% AI alloys using zinc oxide

2021 ◽  
Author(s):  
Subrata K. Saha
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Refinement ◽  
Base Alloy ◽  
Casting Process ◽  
Grain Refiner ◽  
Graphite Mold ◽  
Mold Casting ◽  
Type Fracture ◽  
Proven Method

Grain refinement is a proven method to improve mechanical properties of Mg alloys. In this research, the influence of ZnO on the microstructure of selected magnesium alloys was investigated. For graphite mold casting with an addition of 0.75 wt. % ZnO, the grain size of the AZ91E alloy decreased from 217 μm to 108 μm. For the binary alloy (Mg-9 wt.% Al), the grain size reduced from 288 μm to 93 μm with an addition of 3 wt.% ZnO. No significant fading of ZnO grain refiner was observed for both the alloys. In permanent mold casting process, with an addition of 0.5 wt.% ZnO, the grain size of the AZ91E alloy decreased from 133μm to 79 μm with significant improvements in mechanical properties. Cleavage type fracture was dominant in the base alloy while alloys refined with 0.5 wt.% ZnO showed more quasi-cleavage type fracture.

An Investigation on Duplex Nucleation in AZ91 Magnesium Alloy and Its Influence on High Temperature Mechanical Properties

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
A. Saber ◽  
R. Haghayeghi ◽  
H. Najafi ◽  
Peiman Shahbeigi-Roodposhti
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Grain Refinement ◽  
Al Alloy ◽  
Grain Refiner ◽  
Az91 Magnesium Alloy ◽  
High Temperature Mechanical Properties ◽  
Nucleation Sites ◽  
Refinement Mechanism ◽  
Carbon Inoculation

The grain refinement of Mg–Al alloy AZ91 via carbon inoculation, including the significant role of Mn in advanced nucleation, was analyzed, and the corresponding mechanical properties and aging behavior were investigated. To this end, various amounts of C were added into the liquid at the desired temperatures. Al8Mn5 particles, which are suitable nucleation sites for α-Mg, were identified as the primary grain refiners. In situ particle formation, along with appropriate wetting and a suitable orientation relationship (OR), facilitated the grain refinement mechanism. Al4C3 particles contributed to heterogeneous nucleation by providing suitable Al8Mn5 nucleation sites. Mn removal resulted in poor grain refinement in the Mg–Al alloy. The Hall–Petch relationship, high-temperature tensile behavior, and aging mechanism of the samples refined by 1 wt % C addition (as the best grain refiner) are discussed and compared with industrial practice.

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