Journal of Materials Research and Technology, Vol 26, Iss , Pp 1736-1742 (2023)
Al/Mg bimetallic interface, Al–Mg intermetallic compounds, Ni interlayer, Vibration assisted treatment, Microstructure, Bonding strength, Mining engineering. Metallurgy, and TN1-997
To improve the microstructure of compound casting Al/Mg bimetallic interface and optimize the bonding performance, the vibration assisted treatment and the Ni interlayer coating treatment were combined. After the composite treatment, the thickness of the Al/Mg bimetallic interface decreased significantly, only 8.13% of the original interface thickness. The original large amount of brittle and hard Al–Mg intermetallic compounds (IMCs) no longer existed, and were replaced by the (Mg–Ni) layer dominated by Mg3Ni2Al, the Al3Ni layer and the Ni solid solution layer. The shear crushing effect and the convective stirring effect of the vibration assisted treatment provided more stable and good metallurgical bonding for the Al/Mg bimetallic interface after introducing Ni interlayer. On this basis, combined with the second phase strengthening effect of the newly precipitating Mg3Ni2Al, the bonding strength of the Al/Mg bimetallic interface significantly improved, from 35.47 MPa to 56.12 MPa, with an increase of 58.22%.
Generally, sand casted Al–Li alloy castings have very serious problems in pore defect and interfacial reaction, remarkably weakening the Al–Li alloy castings quality. How to solve these problems is always a challenge. In this paper, a novel inorganic binder coating containing lithium silicate solution binder and silicon carbide powder on the surface of the sand mold was developed to eliminate pore defect and prevent interfacial reaction of the sand casted Al–Li alloy castings. The effective mechanism of the inorganic binder coating on the pore defect and interfacial reaction was discussed. The obtained results showed that the inorganic binder coating formed a thin shell on the surface of the sand mold after pouring, which can effectively prevent the metal-mold interface reaction of the sand casting Al–Li alloy and significantly reduce the porosity defects. Among them, the Al–Li alloy casting prepared using the inorganic binder coating consisting of the lithium silicate binder and silicon carbide powder basically had no pore defects, and the porosity was only 3.73%, which was 66.7% lower than that of the casting prepared by the sand mold without any treatment. Moreover, the interface reaction of the Al–Li alloy and sand mold was fully eliminated, which was attributed to the low overall atomic diffusion rate of the silicon carbide based on molecular dynamics simulation results.
In this work, ultrasonic vibration treatment (UVT) was introduced to improve the interfacial microstructure and bonding strength of A356/AZ91D bimetal processed via lost foam compound casting (LFCC). The interfacial microstructure and mechanical properties of the Al/Mg bimetal processed via LFCC with different UVT durations were investigated. Results revealed the UVT did not change the composition of phases at the interface. The Al/Mg bimetallic interface consisted of an intermetallic compound area (β-Al3Mg2 + γ-Al12Mg17 + Mg2Si) and eutectic area (δ-Mg + γ-Al12Mg17 + Mg2Si). When the duration of the UVT was increased, the gathered Mg2Si particles at the intermetallic compound area were refined to sizes of no more than 5 μm and became more homogeneously dispersed in the intermetallic compound area and diffused in the eutectic area, which could be attributed to the removal of oxide film and the acoustic cavitation and streaming flow effects induced by the UVT. The microhardness of the Al/Mg bimetallic interface was not obviously changed by the increase in UVT duration. The shear strength of the Al/Mg bimetal was increased with UVT and reached maximum with a UVT duration of 5 s, with a value of 56.7 MPa, which was increased by 70.3%, compared with Al/Mg bimetal without UVT. This could be attributed to the removal of the oxide film at the Al/Mg bimetallic interface, which improved the metallurgical bonding of the Al/Mg interface. Additionally, the refined and homogeneously dispersed Mg2Si particles played an important role in suppressing the propagation of cracks and enhancing the shear strength of the Al/Mg bimetal.
In this work, a vibration was applied in the preparation of the Mg/Al bimetal by a novel compound casting in order to improve the mechanical properties of the Mg/Al bimetal, and the effect of the vibration on the interfacial microstructure and mechanical properties of the Mg/Al bimetal was investigated. The results indicated that the vibration had a significant effect on the interfacial microstructure and mechanical properties of the Mg/Al bimetal, but it did not change the phase compositions of the interface, which was composed of layer I (Al3Mg2+Mg2Si), layer II (Al12Mg17+Mg2Si) and layer III (Al12Mg17/δ-Mg). Without vibration, the Mg2Si phase with a needle-like morphology mainly aggregated in the layer II of the interface. After the application of the vibration, the SEM and EBSD analysis results showed that the Mg2Si and Al3Mg2 phases in the interface were obviously refined, and the distribution of the Mg2Si became more uniform, due to the strong forced convection of the molten metal resulting from the vibration. The TEM analysis indicated that the interface between the Al3Mg2 and Mg2Si phases was non-coherent, suggesting the Mg2Si particles cannot act as a heterogeneous nucleation base during the solidification process of the interface. Compared to the Mg/Al bimetal without vibration, the shear strength of the Mg/Al bimetal with vibration increased by about 50% from 31.7 MPa on average to 47.5 MPa, and the hardness of the layer I of the interface increased, and the hardness of the layer III decreased. The fracture surface transformed from a flat fracture morphology without vibration to an irregular zigzag fracture morphology.
Porosity defects and interfacial reaction are very serious problems in sand casting Al–Li alloy, which greatly affect the quality of castings. In this work, the characteristic and formation mechanism of the porosity defects in the sand casting Al–Li alloys were systematically investigated by scanning electron microscopy, transmission electron microscopy, energy spectrometry, and inductively coupled plasma mass spectrometry, in order to provide a theoretical basis for the prevention and control of the pore defects in the sand casting Al–Li alloys. The results found that the Al–Li alloys prepared by metal mold and graphite mold as casting molds had almost no pore defects and interfacial reaction layers, with the porosities of 5.81% and 5.05%, respectively, while the sand casting Al–Li alloys with furan resin, phenolic resin, and sodium silicate binder as binders all had serious pore defects and interfacial reaction layers, with the porosity of 15.67%, sharply weakening the mechanical properties of the Al–Li alloy casting. The types of the pore defects were mainly reactive pores and intrusive pores, and the interface reaction layer was mainly composed of LiAlO2 and C–H–O organics. The formation mechanism of the pore defects in the sand casting Al–Li alloys was caused by the reaction between Li and the hydroxyl groups in the binder of the sand mold to generate a large amount of hydrogen, which intruded into the melt or was sucked into the melt.
Guangyu Li, Wenming Jiang, Feng Guan, Junwen Zhu, Yang Yu, and Zitian Fan
Journal of Magnesium and Alloys, Vol 10, Iss 4, Pp 1075-1085 (2022)
Magnesium/aluminum bimetal, Microstructure, Mechanical properties, Ni coating, Compound casting, High velocity oxygen fuel spraying, Mining engineering. Metallurgy, and TN1-997
In this paper, a Ni coating was deposited on the surface of the A356 aluminum alloy by high velocity oxygen fuel spraying to improve the performance of the AZ91D magnesium/A356 aluminum bimetal prepared by a compound casting. The effects of the Ni coating as well as its thickness on microstructure and mechanical properties of the AZ91D/A356 bimetal were systematically researched for the first time. Results demonstrated that the Ni coating and its thickness had a significant effect on the interfacial phase compositions and mechanical properties of the AZ91D/A356 bimetal. The 10µm's Ni coating cannot prevent the generation of the Al-Mg intermetallic compounds (IMCs) at the interface zone of the AZ91D/A356 bimetal, while the Ni coating with the thickness of 45 µm and 190 µm can avoid the formation of the Al-Mg IMCs. When the Ni coating was 45 µm, the Ni coating disappeared and transformed into Mg-Mg2Ni eutectic structures+Ni2Mg3Al particles at the interface zone. With a thickness of 190µm's Ni coating, part of the Ni coating remained and the interface layer was composed of the Mg-Mg2Ni eutectic structures+ Ni2Mg3Al particles, Mg2Ni layer, Ni solid solution (SS) layer, Al3Ni2 layer, Al3Ni layer and sporadic Al3Ni+Al-Al3Ni eutectic structures from AZ91D side to A356 side in sequence. The interface layer consisting of the Mg-Ni and Al-Ni IMCs obtained with the Ni coating had an obvious lower hardness than the Al-Mg IMCs. The shear strength of the AZ91D/A356 bimetal with a Ni coating of 45 µm thickness enhanced 41.4% in comparison with that of the bimetal without Ni coating, and the fracture of the bimetal with 45µm's Ni coating occurred between the Mg matrix and the interface layer with a mixture of brittle fracture and ductile fracture.
Junlong Wang, Feng Guan, Wenming Jiang, Guangyu Li, Zheng Zhang, and Zitian Fan
Journal of Materials Research and Technology, Vol 15, Iss , Pp 3867-3879 (2021)
Vibration time, Compound casting, Al/Mg bimetallic composites, Interfacial microstructure, Mechanical properties, Mining engineering. Metallurgy, and TN1-997
A simple mechanical vibration was used to enhance interface bonding of the Al/Mg bimetallic composites produced by a novel lost foam compound casting in this study. The effect of vibration time on interfacial microstructure and mechanical properties of the Al/Mg bimetallic composites was investigated. The results show that the vibration time had a significant effect on the interfacial microstructure and mechanical properties of the Al/Mg bimetallic composites. With the increase of the vibration time, the cooling rate during the solidification was increased, and the thickness of intermetallic compounds (IMCs) layer at the interface of the Al/Mg bimetallic composites was decreased. This resulted in the decrease of A3Mg2 and Al12Mg17 brittle phases, and the Mg2Si phase at the interface was refined with a distribution change from agglomeration to dispersion. When the vibration time was 300 s, the vibration fully affected the formation and solidification process of the IMCs layer of the Al/Mg bimetallic composites, and had an obvious effect on the reduction of the brittle phases as well as the improvement of the size and distribution of the Mg2Si phase. As a result, the shear strength of the Al/Mg bimetallic composites was the highest, reaching 47.49 MPa, which was 51% higher than that of the Al/Mg bimetallic composites without vibration.
Repairing the worn surfaces of wear-resistant workpieces, such as rollers, is one of the main application fields of surface treatment, but the repairing time is often not considered. In fact, the repairing time is very important, since it affects the repair quality and service life of wear-resistant workpieces. In this paper, a remelted gradient coating was prepared on a ductile iron plate by plasma transferred arc to simulate the repair treatment of wear-resistant workpieces. First, two positions in the remelted gradient coating were defined, i.e., the top of the gradient remelted layer was defined as M1, and the position where the hardness was two-thirds of the top of the remelting layer was defined as M2. Next, the time taken to repair the workpiece when the working surface reached M2 was proposed. Finally this method was verified by a comparative study on the microhardness and wear resistance of the M1 and M2. In this paper, the M2 was located at a ~0.5 mm from the top of the remelted gradient layer. The results show that the microhardness of the position of the M1 was higher than that of the position of the M2. However, the wear resistance of the M1 was worse, as confirmed by the wear rates. At the same time, cracks and fragments were observed on the worn surface of the M1 and M2 positions. Furthermore, the coefficient of friction (COF) of the position of M1 was noted to be first higher and subsequently lower than that of the position of M2, owing to the grinding ball entering the substrate. The abrasion mechanisms of both regions were observed to be complex, including oxidative wear, adhesive wear, delamination wear, and/or fretting wear. The experimental data indicate that it is feasible to determine the repair time according to the microhardness of workpieces.
In this study, chromium carbide coating obtained by thermo-reactive diffusion (TRD) process on AISI 52100 steel, prepared by packed method at temperature of 850 °C for 2, 4, 6 and 8 h, were investigated by performing a series of tests. The chromium carbide coating was characterized by scanning electron microscopy, X-ray diffraction (XRD), Micro-Vickers hardness test and Daimler-Benz Rockwell-C adhesion test. The chromium carbide layer produced on the AISI52100 steel exhibited a smooth and flat morphology. Depending on treatment time, the coating had a thickness of 3.2 – 8.5 μm. XRD analysis revealed the existence of Cr7C3 and (Cr,Fe)7C3 compounds. The hardness of the surface was increased from 723 to 1730 – 1920 HV0.025 after the coating process. The adhesion strength quality of the coating is correlated to HF2 to HF3 according to the VDI 3198 norm. Comparision of wear performance between chromium carbide coating and substrate showed that the coating can significantly improve wear resistance of the material. Friction coefficient decreased from the 0.46 to 0.37 and wear weight loss decreased by 89.3 %.
Guanjin Li, Shiyan Tang, Li Yang, Lei Qian, Fuchu Liu, Zitian Fan, Kang Zuo, Qingsong Wei, and Wenming Jiang
Materials & Design, Vol 183, Iss , Pp - (2019)
Materials of engineering and construction. Mechanics of materials and TA401-492
The support material is necessary to prevent the collapse of the suspended structure when forming complex ceramic parts via layered extrusion forming (LEF, a type of additive manufacturing) method, and needs to be removed easily after sintering. In this work, salt-based slurries were prepared with magnesium sulfate monohydrate (MSM) and polyvinyl pyrrolidone (PVP) in order to solve the problem of extrusion and removal of the support material. The effect of the solid content on the rheological performance of slurries and the printing quality of specimens was studied. The results showed that the salt-based slurry containing 60 wt% MSM and 10 wt% PVP powder possessed shear-thinning behavior and the corresponding samples held sufficient bending strength and superior surface quality, which satisfied the requirements for the support structures in LEF method. After calcination at different temperature, the salt-based support structure could be easily removed, which offers an alternative support material choice for the LEF method. Keywords: Layered extrusion forming, Salt-based slurry, Magnesium sulfate, Rheology, Soluble support material
used sodium silicate sand, dry reusing, wet reclaiming, Technology, Manufactures, and TS1-2301
Based on the characteristics of used sodium silicate sand and the different use requirements for recycled sand, "dry reusing and wet reclaiming of used sodium silicate sand" is considered as the most suitable technique for the used sand. When the recycled sand is used as support sand, the used sand is only reused by dry process including breaking, screening, dust-removal, etc., and it is not necessary that the used sand is reclaimed with strongly rubbing and scraping method, but when the recycled sand is used as facing sand (or single sand), the used sand must be reclaimed by wet method for higher removal rate of the residual binders. The characteristics and the properties of the dry reused sand are compared with the wet reclaimed sand after combining the different use requirements of support sand and facing sand (or single sand), and above the most adaptive scheme has also been validated.
Using a special coated sand as the material of the selected laser sintering (SLS), the authors test and nvestigate the strength change of the test samples in terms of different sintering parameters (scanning speed, laser power, sintering thickness, and so on). The characteristics of coate sand hardening by laser beam are analyzed. The sitered mold (or core) for given casting is poured with molten metal.
Based on Vacuum Differential Pressure Casting (VDPC) precision forming technology and the Selective Laser Sintering (SLS) Rapid Prototyping (RP) technology, a rapid manufacturing method called Rapid Precision Casting (RPC) process from computer three-dimensional solid models to metallic parts was investigated. The experimental results showed that the main advantage of RPC was not only its ability to cast higher internal quality and more accurate complex thin-walled aluminum alloy parts, but also the greatly-reduced lead time cycle from Selective Laser Sintering(SLS) plastic prototyping to metallic parts. The key forming technology of RPC for complex thin-walled metallic parts has been developed for new casting production and Rapid Tooling (RT), and it is possible to rapidly manufacture high-quality and accurate metallic parts by means of RP in foundry industry.
rapid prototyping, selected laser sintering, laser scanning, part accuracy, Technology, Manufactures, and TS1-2301
The effects of different factors, including the precision of the selected laser sintering (SLS) equipment, sintering temperature, sintered thickness of individual layer and laser scanning route, on the SLS part accuracy have been analyzed and studied. Some measures are suggested in order to improve the part accuracy made by SLS.