In this study, AlSiMgMnCu alloys with different Cu and Mg contents were fabricated by high vacuum die casting (HVDC) technique. The phase formation and their microstructure evolution are ...quantitatively studied by serial block-face scanning electron microscopy (SBFSEM) at nano-scale in three-dimensions. Through analyzing their three-dimensional (3D) microstructure, effects of the spatial distribution, volume fractions and morphology of the intermetallic phases on the alloy’s mechanical properties are comprehensively discussed. It is found that, with higher Cu content and lower Mg content, the nucleation and growth of θ-Al2Cu phase would have advantage over Q-Al5Cu2Mg8Si6 phase. In contrast, decreasing Cu/Mg ratio by increasing Mg content is in favor of the nucleation and growth of the Q-Al5Cu2Mg8Si6 phase. The uniformly distributed fine θ-Al2Cu phase provides the highest contribution to the strengthening of the HVDC AlSiMgMnCu alloys. For the Cu/Mg ratio to be 3, an as-cast HVDC Al-10Si-0.2Mg-0.5Mn-0.6Cu alloy with optimized ultimate tensile strength, yield strength and elongation of 330 MPa, 162 MPa and 10.2%, respectively, had been produced.
•3D microstructure of HVDC AlSiMgMnCu alloys with different Mg and Cu contents were quantitatively analyzed by SBFSEM.•Adding Cu enhances the growth of θ phase, and adding Mg enhances the growth of Q phase along the grain boundaries.•Fine and uniformly distributed θ phases make the highest contribution to the strengthening of HVDC AlSiMgMnCu alloys.
The AlSiMgMn alloys with different Fe and Mn contents were prepared with high vacuum die casting (HVDC) process. The Fe-rich intermetallics in the surface layer and center of the alloys were ...inspected with high-resolution 3D X-ray micro-computed tomography (μ-CT), and the growth mechanism of the primary Fe-rich phase was analyzed through their different 3D morphographies. By combining Bisecting K-means and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) methods, the intermetallic clusters in the surface layer and center were quantified. The results show that the primary Fe-rich intermetallics were characterized as hexahedron and octagonal dendrite shapes with large size while the eutectic Fe-rich intermetallics were polyhedron and Chinese-script shapes. When Fe and Mn contents of the alloys were lower, the intermetallic clusters in the surface layer were with less cluster number and larger intermetallic distances showing uniform distribution whereas the clusters in the center were more and had shorter distances. In the case of alloys with higher Fe and Mn contents, the intermetallics showed clustering distribution in both the surface layer and center. The mechanism for the intermetallic cluster formation in the surface layer and center was further discussed.
•The growth of primary Fe-rich intermetallic in die-cast AlSiMgMn alloys was proposed through 3D morphologies of intermetallics inspected by μ-CT.•The characteristics of Fe-rich intermetallic clusters were quantified by the combination of Bisecting K-means and DBSCAN methods.•The effects of different primary phases on the Fe-rich intermetallics and the formation of intermetallic clusters were analyzed.
Quenching cooling rate in solution treatment is the decisive parameter for solute supersaturation and mechanical properties after following aging of wrought and casting Al alloys. In this study, the ...microstructure quantitative characteristics, mechanical properties and residual stress of high vacuum die casting (HVDC) AlSi10MgMn alloys with different cooling rates during spray quenching were comprehensive studied, which were compared with the conditions of air and wind cooling as well as water quenching. The results showed that, with the decrease of quenching cooling rate, the cross-section diameters of the nano-precipitates β" increased, the precipitates number density decreased in the aged alloys, and the precipitate free zone (PFZ) at grain boundary widened. In addition, β' and β phases appeared in the samples quenched by air and wind. As the cooling rate dropped, the ultimate tensile strength (UTS) and yield strength (YS) of as-aged alloys decreased whereas the elongation (EL) increased, and the quenching residual stress declined. A critical quenching cooling rate over 30 °C/s followed with aging treatment was found for strengthening the AlSi10MgMn alloys and reducing quenching residual stress. The results are important for controlling mechanical properties and residual stress in the alloy practical application.
•The heat transfer behavior of high vacuum die casting AlSi10MgMn alloys during spray quenching at different spray parameters was analyzed.•The effects of quenching cooling rates on β″ precipitates and PFZs in microstructure were investigated.•The critical cooling rate to balance mechanical properties and residual stress is 30 ℃/s for the alloys.
The present research aim is to synthesize the aluminum alloy hybrid composite by using different weight percentages of SiC (0wt%, 5wt%, 10wt%, & 15wt%) and Al
2
O
3
(0wt%, 9wt%, 7wt%, and 5wt%) ...nanoparticle blended with 500 rpm and 700 rpm stir speed via stir casting route assisted with vacuum die casting (2 × 10
5
bar) to limit the porosity and enhance the density, hardness, impact, yield, and tensile strength of the composites. The influences of stir speed on SEM, physical, and mechanical behavior of the aluminum hybrid composite was experimentally studied. The SEM micrograph revealed the homogenous particle distribution proved with good interface bonding between matrix and reinforcement. The investigation results of the hybrid nanocomposite prepared by 700 rpm stir speed with inversely increased content of SiC and Al
2
O
3
show decreased porosity percentages of less than 1%,and its density was increased nominally. The composite containing 15wt% SiC and 5wt% Al
2
O
3
is found to have superior mechanical properties as the hardness, impact, and tensile strength are enhanced by 49.2%, 20.47%, and 33.15% as compared to Al–Mg cast alloy. Finally, the developed hybrid aluminium alloy composite with exemplary behaviour is recommended for steel bridge construction applications.
•SiO2/TiO2 was evenly diffused with Al5754 alloy at 800 °C, 650 rpmfor 20 min.•Reduction in grain size (±3μm), improves mechanical properties of hybrid blends.•Improves tensile (34.65%) and ...compressive (36.51%) strength to Al5754 alloy.•Enhanced grain refinement improves, work hardening, flexural and impact strength.•Interphase of immixture improves oxide layer (40.03%) and reduces O2 permeability.
In the present investigation, SiO2/TiO2/Al5754 alloy hybrid composites were synthesised using vacuum die-casting, and their morphology, mechanical, wear, and corrosion properties were analyzed. The strengthening particles are evenly diffused with Al5754 alloy at 800 °C, 650 rpm, and 20 min without residual pores. Due to a reduction in grain size, enhanced wettability, and intrinsic oxidation characteristics, the synthesised immixture exhibits an increase in hardness (32.04 %), tensile (34.6 %), and compressive strength (36.51 %) in context with as cast alloy. The interphase of hybrid blends Al2Si2O7, Mg2Si, andAl2O3 limits oxygen permeability and increases corrosion resistance (40.03 %). By increasing the applied load, the wear loss percentage decreased due to higher stresses and intense plastic deformation at the contact interface.
Al–Si–Mg cast alloys can be imparted with a wide range of mechanical properties through heat treatment, thus meeting the required performance of various vehicle components. However, because of the ...characteristics of the high-pressure die casting process, the gas porosities in the casting can lead to blisters during the solution treatment of die-casting parts. Therefore, systematic studies on the solution temperature and solution time are required to prevent such blisters. In this study, the gas porosity and mechanical properties of T6 heat-treated specimens were evaluated under various solution treatment conditions. As the solution treatment temperature and time increased, the numbers and volume of individual gas porosity increased. On the other hand, there were little changes in the shrinkages upon heat treatment. As solution temperature and time increased, the area fraction of the eutectic Si particles and Mg2Si decreased slightly, whereas the area and sphericity of the eutectic Si and Mg2Si increased. As the solution treatment temperature and time increased, the ultimate tensile strength and yield strength increased, whereas the elongation tended to decrease. However, the maximum UTS and YS were obtained on treatment at 520 °C for 1.5 h.
•Vacuum die casting of Al–Si–Mg alloy under solution treatment conditions.•Separation of gas porosities and shrinkage and their quantitative measurement.•Mechanical property comparison between T6 heat-treated and as-cast specimens.
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•Spatial structure at nano-scale of the eutectic Si, α-Fe, β-Mg2Si, Q-Al5Cu2Mg8Si6 and θ-Al2Cu phases before and after the T6 heat treatment were revealed by SBFSEM and quantitatively ...analyzed.•The solute solution is firstly calculated via SBFSEM measurements based on mass conservation.•The optimized trade-off between strength and ductility can be achieved by generation of fine and high density nano-precipitated phases via the T6 heat treatment.
A method to calculate element concentrations in Al alloy castings, based on the serial block-face scanning electron microscopy (SBFSEM) measurement at nano-scale, was proposed. For the high vacuum die casting (HVDC) Al-10Si-0.4MgMn-0.6Cu alloy, it reveals that the solute fractions of the Si, Mg and Cu in the Al matrix reaches about 0.39 wt%, 0.15 wt%, and 0.10 wt%, respectively, under the as-cast condition. After it was heat treated via T5 process, larger nano-scale precipitation phases with low density and non-uniform distribution were formed in the α-Al matrix. After T6-treated, the narrow neck regions of the seaweed-like α-Fe phase particles were fragmented as well, but could not dissolve into the α-Al matrix. The element concentrations of the Si, Mg and Cu in the α-Al matrix increases to 0.75 wt%, 0.23 wt%, and 0.43 wt%, respectively. Hence, finer nano-scale precipitation phases with high density and uniform distribution are formed in the Al matrix. Consequently, the ultimate tensile strength, yield strength and elongation of the T6-treated alloy simultaneously increase of about 15%, 52% and 63%, respectively. It presents that the solute solution during high pressure die casting solidification has decisive effect on the mechanical properties before and after heat treatment.
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Two-stage super vacuum (19 mbar) assisted high pressure die casting (HPDC) was achieved by evacuating from the die cavity and the shot sleeve simultaneously. The effect of super ...vacuum assisted HPDC on the repeatability of the tensile properties of Al-Si-Mg-Mn die-cast alloy was investigated in comparison with conventional HPDC. The quantitative Weibull analysis confirmed that super vacuum assisted HPDC improved the repeatability of the tensile properties of the alloy. The data and deviation analysis verified that super vacuum assisted HPDC considerably decreased the fluctuations of the ductility of the alloy by 71% in as-cast state and 84% after solution and ageing treatment. The results also showed that super vacuum assisted HPDC improved the ultimate tensile strength and ductility of the as-cast alloy by 5.6% and 43%, respectively, and increased the ductility of the alloy by 21% after solution and ageing treatment. The significant improvements of ductility and the repeatability of tensile properties were originated from the decrease of porosity volume fraction and porosity size in the alloy processed by super vacuum assisted HPDC. The reduction of defect size can improve the stress distribution and retard the crack initiation in castings. Therefore, the tensile strength and ductility were enhanced in the die-cast alloy processed by super vacuum assisted HPDC.
The effects of Cu content and heat treatment process on the microstructures and mechanical properties of a series of Al−Si−Mg−Mn−xCu cast aluminum alloys prepared by the vacuum die casting process ...were investigated by three-dimensional X-ray microscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy and microhardness testing. It was found that the number density and size of gas porosities increase with increasing Cu content. However, the Cu addition will promote the formation of Cu-containing primary phases (Q-Al5Cu2Mg8Si6 and θ-Al2Cu) during the solidification, which will improve the properties of the alloys. Five different primary phases were observed, namely eutectic Si, α-Al(Fe, Mn)Si, β-Mg2Si, Q-Al5Cu2Mg8Si6, and θ-Al2Cu phases. With increasing the Cu content, the θ phase area fraction increases significantly, while the α-Al(Fe, Mn)Si phase area fraction decreases initially, followed by a slight increase, with the Q phase area fraction displaying the opposite trend relative to α-Al(Fe, Mn)Si phase. These primary phases present different evolution rules during heat treatment process. During subsequent aging, the synergic effect of precipitating Q' and θ' phases can significantly increase the alloy hardening response.
•In-situ bulk metallic glass composites (BMGCs) with excellent ductility and work hardening were successfully developed using a low vacuum high pressure die casting (LV-HPDC) technology along with ...industrial grade raw materials.•The LV-HPDC method shows a smaller volume fraction difference of the dendrite phase for BMGCs with the same composition, although the size of the β-phase is generally larger compared to the copper mold suction casting method.•The ductility of the BMGCs prepared by LV-HPDC can be maintained if two conditions are met: (1) the volume fraction of β phase stays below 62% ± 2%, and (2) the appearance of the dendritic phase satisfies a size uniformity.
The glass-forming ability and mechanical properties of metallic glasses and their composites are well known to be sensitive to the preparation conditions and are highly deteriorated by industrial preparing conditions such as low-purity raw materials and low vacuum. Here, we showed that a series of in-situ bulk metallic glass composites (BMGCs) which exhibit excellent ductility and segmental work hardening were successfully developed utilizing a high vacuum high-pressure die casting (HV-HPDC) technology along with industrial-grade raw materials. The tensile properties of these BMGCs are systematically investigated and correlated with the alloy microstructure. As compared with the copper mold suction casting method, the volume fraction difference of the dendrite phase for the BMGCs with the same composition is not significant when fabricated by the HV-HPDC, whereas the size of the β-phase is generally larger. In-situ BMGCs with the composition of Ti48Zr20(V12/17Cu5/17)19Be13 obtained by the HV-HPDC process show ductility up to 11.3% under tension at room temperature and exhibit a certain amount of work hardening. Two conditions need to be met to enable the BMGCs, which are prepared by vacuum die-casting to retain favorable ductility: (1) The volume fraction of β phase stays below 62% ± 2%; (2) The equiaxed crystals with a more uniform size in the range of 5–10 μm. Meanwhile, the results of the present study provided guidance for developing BMGCs with good ductile properties under industrial conditions.
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