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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.
A series of Al-xCe (x = 2, 4, 6, 8, 10 wt%) and Al–8Ce-yMg (y = 0, 0.10, 0.25, 0.50, 0.75 wt%) alloys were prepared by high-pressure die casting. The introduced cerium element promoted the nucleation ...of α-Al grains. Al11Ce3 phase served as the heterogeneous nucleation substrate of α-Al due to the small lattice mismatch of 6.72%. According to the results calculated by Nelson-Riley extrapolation function, the lattice constant of α-Al increased from 4.0511 Å to 4.0540 Å with the increasing of Mg content from 0 wt% to 0.75 wt%. Due to the solid solution strengthening effect of Mg atoms, the yield strength of Al–8Ce-yMg alloys and the hardness of α-Al matrix in the Al–8Ce-yMg alloys showed a parabolically increasing tendency, from 92 MPa to 115 MPa and 0.502 GPa–0.575 GPa, respectively. The work hardening capacity of Al–8Ce-yMg alloys was improved by the solid solution of Mg with the work hardening exponent increasing from 0.21 to 0.27. The solid solution of Mg atoms reduced the stacking fault energy of Al–8Ce-yMg alloys and suppressed the dynamic recovery process of the alloys during deformation process, which promoted the formation of dislocation tangles and dislocation networks in the α-Al matrix.
•Al11Ce3 could act as the heterogeneous nucleation substrate of α-Al due to the small lattice mismatch of 6.72%.•The lattice constant of α-Al increases from 4.0511 Å to 4.0540 Å due to the solid solution Mg atoms.•Solid solution strengthening of Mg improves the yield strength of Al–8Ce-yMg alloys and the hardness of α-Al matrix.•Solid solution of Mg reduces the stacking fault energy and suppresses the dynamic recovery process of Al–8Ce-yMg alloys.
A high strength (Yield strength ≥ 320 MPa) and high ductility (Tensile elongation ≥ 10%) die–cast aluminium alloy was first developed. The AlSiCuMgMn alloy processed by high pressure die casting can ...provide the high yield strength of 321 MPa, the high ultimate tensile strength of 425 MPa and the high ductility of 11.3%, after solution treated at 510 °C for 30 min and aged at 170 °C for 12 h. The alloy demonstrated 150% increase in ductility over the reported most advanced die–cast aluminium alloy, also comparable tensile properties to the 6000 series wrought aluminium alloys but with much lower manufacturing cost. The as–cast microstructure of the alloy mainly contained the primary α1–Al phase solidified in the shot sleeve, the secondary α2–Al phase solidified in the die, the Al–Si eutectic phase and the intermetallic phases Q–Al5Cu2Mg8Si6 and θ–Al2Cu. The intermetallic phases Q and θ were dissolved into the α–Al matrix during solution. Nanoscale precipitates Q′ and θ′ were precipitated from the α–Al matrix for the strengthening of the alloy through ageing treatment. Multiple effects resulted in the high ductility of the alloy.
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•Advanced die–cast Al alloy was developed with high strength and high ductility.•The developed alloy provides YS of 321 MPa, UTS of 425 MPa and ductility of 11.3%.•The developed alloy demonstrates 150% increase in ductility over the current alloys.•The developed alloy demonstrates comparable tensile properties to wrought Al alloys.•The developed alloy demonstrates milestone tensile properties for HPDC industry.
Microstructure and mechanical properties of a newly developed Al–4Mg–2Fe alloy prepared via high pressure die casting (HPDC) were studied. Attention was focused on the characteristics of the ...iron-rich intermetallic compounds (IMCs) and their influence on crack initiation and propagation. Result shows three types of iron-rich IMCs (Al13Fe4) existed in the alloy. The first is the primary iron-rich IMCs (P-IMCs) precipitating prior to the α-Al phase. These IMCs comprised external solidified iron-rich IMCs (P-IMC)I forming inside the shot sleeve and secondary iron-rich IMCs (P-IMCs)II inside the cavity. The second is fine ternary eutectic iron-rich IMCs (TE-IMCs), one of the phases of the ternary Al–Al8Mg5–Al13Fe4 eutectic. The third is binary eutectic iron-rich IMCs (BE-IMCs), which formed between P-IMCs and TE-IMCs via binary eutectic reaction: L→Al + Al13Fe4. Accordingly, the (P-IMCs)I acted as crack initiation sources regardless of the orientation due to the extremely large size and aspect ratio. The (P-IMCs)II exhibiting a large aspect ratio but small size accelerated the crack propagation. The BE-IMC and TE-IMCs, due to the tiny small size and aspect ratio, barely exhibited any effect on the final failure.
•Influence of HPDC solidification behavior of AlMg4Fe2 alloy on iron-rich intermetallic compounds (IMCs) was studied.•Three types of iron-rich IMCs were observed, and the corresponding effect on the mechanical properties was discussed.•3-D large size reconfiguration technology was performed to characterize the size and morphology of iron-rich IMCs.•The influence of iron-rich IMCs on crack behavior was dependent on the size and morphology regardless of orientation.
The characterization of externally solidified crystals (ESCs) and porosities in a high-pressure die-cast AlSi10MnMg alloy was investigated using optical microscope (OM) and computed tomography (CT) ...with particular attention on the effect of shot speeds on the ESCs and fracture behavior. Results showed that ESCs tended to agglomerate at the center region and changed from fine globular grains into large size dendrites from surface to center. The formation of the ESCs is found to be coarser as the "slow shot speed" in the first stage of high-pressure die casting (HPDC) or the "fast shot speed" in the second stage of HPDC is reduced, consequently, the corresponding ESC area fraction increased. From the fractured morphology, the plate specimen with a higher ESC content exhibited a rough fracture and a large volume fraction of shrinkage porosities was discovered beneath the fracture surface especially when a lower fast shot speed was applied. In in-situ tensile test, the large size shrinkage porosity served as a crack source and it further expanded in an inter-granular mode along ESC boundaries/other porosities (which caused a tortuous crack route) or in a trans-granular mode across the ESC grains/fine (α-Al)II grains (which caused a flat crack route). In addition, the gas porosities in the specimen promoted the crack propagation as a crack concentration area and experienced almost no deformation during the tensile process.
Chemical composition of secondary Al-Si-Cu alloys and working variables of high-pressure die casting process (HPDC) may change for the same casting parts from one country to another in the world. ...They can even sometimes vary from one manufacturing site to another within the same country. An experimental study on the influence of alloying elements contents (Si and Cu), casting temperature and injection pressure on mechanical properties of die cast aluminum alloys was carried out to support the automotive industry suppliers in designing their cast parts. The microstructural features and the porosity level were also investigated and assessed. The primary objective is to highlight the modification mechanisms of the achieved properties using tensile tests, hardness measurements and microstructural observations performed on a HPDC casting parts. Low pressure and low temperature increase the rate of porosity, promote the formation of coarse Fe-rich intermetallic compounds and change the morphology of α-Al phases. These in turn deteriorate mechanical tensile properties. However, variation of alloying elements contents modifies the optimum properties achieved when part is made at constant casting processing parameters. Finally, the interactions between the studied parameters of HPDC and the chemical alloying elements show also a significant influence on the tensile properties.
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Aimed at the mechanical property improvement in the high pressure die casting (HPDC) process for the aluminium alloy, two sets of shot curves (the baseline and the optimized ...condition) are designed to study their influence on the distributions of the ultimate tensile strength (UTS) and the elongation (El) for the as-cast ASTM tensile samples. Difference in the as-cast microstructures and defects are characterized and compared accordingly. Following the experiments, a mathematical model for the entire HPDC process is established to study the characteristics of the melt flow, heat transfer, solidification and defects formation (entrapped gas, oxides, porosities) during the HPDC process with the two above-mentioned piston shot curves are analyzed. The results have shown that the UTS and the El are improved obviously with the optimized shot profile. And the mechanism for these changes are explained in detail. This work provides a novel approach for designing and optimization of metal casting process without conducting excessive experiments and it could be transferred and applied to various alloys systems and different casting processes.
This work systematically investigated the microstructure and mechanical properties of Mg-xGd-3Y–1Zn-0.4Zr (wt%) alloys prepared via rheo-diecasting (RDC) in comparison to those of conventional high ...pressure die casting (HPDC) alloys, and revealed their differences in microstructure, casting defects, and mechanical properties. The microstructure of the as-cast RDC Mg-xGd-3Y–1Zn-0.4Zr (wt%) alloys is primarily composed of α-Mg and Mg3(Gd,Y,Zn) eutectic phases. Of the four alloys studied, the GWZ831K and GWZ1431K alloys exhibit the best elongation (EL: 6.4±1.3 %) and the highest strengths (UTS: 270±9 MPa; YS: 201±5.7 MPa), respectively. The GWZ831K alloy exhibits a quasi-cleavage fracture during room-temperature tensile tests, whereas the GWZ1431K alloy demonstrates a brittle fracture. The phase composition of conventional HPDC alloys is fundamentally the same as that of RDC alloys, but their grains and eutectic phases differ in morphology and are smaller in size. Oxide films are frequently found in conventional HPDC castings, but neither oxide films nor pore defects are observed in RDC alloys. Compared to conventional HPDC alloys, RDC alloys have better elongation but lower strength. The lower strength of RDC alloys compared to HPDC alloys can be attributed to larger grains and eutectic phases, along with fewer stacking faults (SFs), resulting in limited strengthening effects of grain boundaries, eutectic second phases and SFs. In contrast, RDC alloys exhibit superior elongation compared to HPDC alloys due to the elimination of oxide films and pore defects, as well as the excellent ductility of the α-Mg matrix that can effectively coordinate deformation.
•Rheo-diecast Mg-Gd series alloys and HPDC counterparts were successfully prepared.•Rheo-diecasting eliminates the RE oxide film defects often found in HPDC alloys.•HPDC alloys have more stacking faults and finer grains than rheo-diecast alloys.•Rheo-diecast alloys show better elongation but lower strength than HPDC alloys.
The morphological properties and distribution characteristics of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated by synchrotron X-ray tomography ...technology. Attention was focused on the formation and evolution mechanism of primary iron-rich intermetallic compounds (IMCs) in high pressure die casting (HPDC). Results show that two different sizes of primary iron-rich phases included externally solidified primary iron-rich phase I ((P-IMC)I) and primary iron-rich phase II ((P-IMC)II). The morphology of (P-IMC)I was close to a hexahedron while (P-IMC)II was nearly a spherical particle. Both (P-IMC)I and (P-IMC)II enriched in the central area and their volume fraction maintained a high level from defect band to center. Phase calculation show that (P-IMC)I (601 °C) preferentially precipitated from liquid and its further growth led to the decrease of Mn/Fe ratio in the subsequent formed (P-IMC)II. In HPDC solidification process, (P-IMC)II exhibited a lateral growth pattern with the terminating surfaces determined to be {1 1 0} planes. In addition, the hexahedral (P-IMC)I in central ESCs-rich zone developed into a dendrite along its corner direction.
•The primary iron-rich phase in a HPDC hypoeutectic Al-Si alloy is study.•3-D morphology of primary iron-rich phases are investigated by synchrotron X-ray tomography.•(P-IMC)II exhibits a lateral growth pattern.•(P-IMC)I in central ESCs-rich zone develops into a dendrite along its corner direction.
Defect-free Friction stir welded joints between the AZ91 Mg alloy and A383 Al alloy were obtained at a welding speed of 40 mm/min and a rotational speed of 900 rpm. Mg and Al were intermixed and ...presented intercalated strips microstructure. The second phases Si, Al3Mg2, Al12Mg17 and Mg2Si distributed uniformly in stir zone at a rotational speed of 900 rpm, and there is a narrow intermetallic compounds layer (∼10 μm) at the interface of the two base metals. The tensile strength of the dissimilar AZ91/A383 joint is 93 MPa, which is approximately 45% of the A383 alloy. The sufficient material intermixing and uniform distribution of second phases are helpful to the joint properties.
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