An air-cooled stirring rod (ACSR) process for efficiently preparing large volumes of semisolid slurry was introduced. A new low-cost casting Al–Si–Fe–Mg–Sr alloy was used to prepare large thin-walled ...heat-dissipating shells using both conventional HPDC and ACSR rheological high pressure die-casting (Rheo-HPDC) technologies. Their microstructures, thermal conductivities, elevated temperature and room temperature mechanical properties, and corrosion behaviors were compared. Furthermore, this work analyzed the mechanisms responsible for the microstructure refinement and performance enhancement in ACSR Rheo-HPDC alloys. The results showed that only 25 s was needed to prepare 32 kg of the semisolid slurry using ACSR process. The alloy prepared by ACSR Rheo-HPDC generated a large number of fine spherical primary α-Al particles with a volume fraction greater than 40%. The Rheo-HPDC alloy showed a moderate strength, high plasticity, and high heat conductivity. The heat conductivity, ultimate tensile strength and elongation of the Rheo-HPDC alloy were 184 W/(m.K), 264 MPa and 12.2% respectively, while those of the HPDC alloy were 167 W/(m.K), 228 MPa and 5.8% respectively. The improvement of heat conductivity of the alloy formed via ACSR Rheo-HPDC was mainly ascribed to the decrease of electron scattering by the refinement of eutectic silicons and Fe-rich intermetallics. This allowed the electron flow to pass through the eutectic Si region more easily. The refined and uniformly-distributed heat-resistant β-Al5FeSi intermetallics effectively prevented grain boundary sliding, so the Rheo-HPDC alloy showed superior high-temperature mechanical properties. The Rheo-HPDC alloy presented a more excellent corrosion resistance to the conventional HPDC alloy due to the refinement of iron-rich phase and eutectic silicons and the reduction in the potential difference between the matrix and the iron-rich phase.
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Cerium-based conversion coatings were deposited on Rheo-High Pressure Die Cast (HPDC) Al-Si alloys by immersion in cerium nitrate aqueous solutions. Rheocast Al-Si alloys have a ...heterogeneous microstructure and present a challenge for the conversion treatment. Different parameters were studied to optimize the conversion coating, and NaCl or H2O2 were also added to the solution to modify or accelerate the deposition process. The mechanism of the coating formation was studied by means of focused ion beam milling (FIB) assisted SEM. The results show that applying cerium-based conversion coating to Al-Si alloys, is possible and a preferential deposition is obtained due to the presence of iron-rich intermetallic particles inside the eutectic region. The formation mechanism of selectively deposited cerium-based conversion coating includes dissolution of aluminium matrix, selective dissolution of aluminium from the noble intermetallic particles, oxidation of iron from the intermetallic particles, and the deposition of cerium hydroxide/oxide layer. The results reveal that the improvement in corrosion resistance in the presence of selectively deposited cerium-based conversion coating is more significant compared to the homogenous coating deposited from the conversion solution containing H2O2.
The microstructures, mechanical properties, thermal conductivities, and corrosion behavior of novel high-thermal-conductivity hypoeutectic Al-Si alloys, prepared by rheological high-pressure ...die-casting (Rheo-HPDC) and HPDC, were investigated and compared. The microstructure of the Rheo-HPDC alloy, including the primary α-Al (α1), secondary α-Al (α2-Al), β-Al5FeSi, and Si phases, was significantly more refined than that of the HPDC alloy. Compared to the HPDC alloy, the Rheo-HPDC alloy exhibited superior mechanical properties and thermal conductivity, and its ultimate tensile strength (UTS), yield strength (YS), elongation, hardness, and thermal conductivity were improved by 27%, 21%, 72%, 10% and 8%, respectively. Pitting corrosion of the Rheo-HPDC alloy was observed to originate at the interfaces between the Fe-rich intermetallics and the α2-Al particles. Corrosion was observed to propagate in the eutectic areas upon prolonged immersion in 3.5 wt% NaCl solution. Electrochemical testing, scanning Kelvin probe (SKP) measurements, and corrosion-morphology analyses reveal that the Rheo-HPDC alloy has better corrosion resistance, primarily due to the decrease in the potential difference between the Fe-rich intermetallics and the matrix, the refinement of the eutectic Si and intermetallics, and the decrease in the areal ratio of eutectic Si to α2-Al.
•The microstructure of the Rheo-HPDC Al-Si alloy is remarkably refined compared to its HPDC analog.•The mechanical properties and thermal conductivity of the Rheo-HPDC alloy are superior.•The Rheo-HPDC alloy exhibited better corrosion resistance than the HPDC alloy.•Pitting originates at the Fe-rich-intermetallics/α2-Al particle interface.
•A simple and efficient DCC process to prepare semisolid slurry was developed.•The semisolid viscosity model of A356 alloy was fitted.•The microstructure of the DCC Rheo-HPDC alloy was greatly ...refined compared to its HPDC analog.•DCC Rheo-HPDC alloy showed better mechanical properties than the HPDC alloy.•The nucleation mechanism and growth law of primary grain in DCC were clarified.
A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size < 50 μm, a shape factor >0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.
In the modern competitive world environment, the foundry industry must efficiently perform with very few rejections. The casting process is completed in three steps: pre-casting, casting, and ...post-casting. The primary casting Process involves charging the furnace, melting metal, holding it at certain temperatures, and pouring operation. The post-casting includes inspection and dispatch. The industry focuses on lower manufacturing costs with high productivity. Manufacturing high-quality products in less time without any defects is a goal of every foundry industry. Various casting defects such as shrinkage, porosity, surface finish, cold shut, and extra material are common. There is a direct impact of these defects on an organization’s quality, productivity, and profitability. Castings without any defect and minimum cost of production are desired for the foundries.
In the present case study, data is collected from the foundry. The study of various causes of defects and product rejection during the High-Pressure Die Casting (HPDC) is conducted. Cylinder block castings was selected for analysis which are made up of aluminum alloy used in engines of automobiles. Defects in casting are the limitations of the casting process. This study provides knowledge of casting defects and their root cause analysis. This paper uses the Pareto analysis technique to identify the primary defects. The critical areas are identified through the case study and prioritization of casting defects. The casting defects observed are arranged in decreasing order and discovered that 80% of rejections are due to casting defects like cold shut, shrinkage, soldering, stain, crack, and warpage. Further, a cause-and-effect analysis is conducted. The reasons have the most significant effects and suggestions are claimed for improved casting quality in the future.
A newly developed Mg-4Zn-2La-3Y alloy with high strength was fabricated by high-pressure die casting method, and its microstructures were thoroughly studied using transmission electron microscopy. ...The results demonstrate that it owns fine grains and approximately highly interconnected intermetallic phase skeletons, and exhibits ultra-high strength at both room and high temperatures. Interestingly, the eutectic intermetallic skeleton of this alloys is consisted of numerous fine particles, which are mainly consisted of two intermetallic phases, namely W and Mg12RE. Multiple {101} twins and SFs were found in the Mg12RE phase while a few of SFs in the W phase. Additionally, minor long-period stacking ordered phase was observed in the eutectoid phase, and it probably nucleated on the Mg12RE phase following a certain OR as (0002)14H//(110)Mg12RE and 112¯014H//11¯1¯Mg12RE, or (0002)14H//(211)Mg12RE and 112¯014H//11¯1¯Mg12RE. This special intermetallic skeleton with many interfaces and planar faults can efficiently transfer dislocations across grain boundaries, and this is the key factor for the outstanding mechanical properties of the studied alloy.
•The porosity distribution inside a porous AM60 sample is investigated via XRT.•The DIC strain mapping was used to verify the reliability of the FE result which contains 6813 pores with various ...characteristics.•The local stress/strain in the vicinity of large pores evolves progressively along with deformation.•The harmfulness of individual pores located in defect bands of HPDC AM60 alloy is firstly evaluated through finite element analysis.
Casting pores are regarded as the main factor causing stress/strain concentrations, facilitating the initiation of microcracks and shortening the plasticity of a cast component. The influence of pore characteristics (i.e., size, morphology, and position) on local stress concentration in a High Pressure Die Cast (HPDC) AM60 sample is studied utilizing X-ray tomography (XRT) and image-based finite element (FE) techniques. Heterogeneous porosity distribution is identified in terms of volume fraction and projected area ratio per segment. Statistically results demonstrate that small pores (volume < 0.01 mm3) have higher number frequency and sphericity. In contrast, large pores (volume > 0.01 mm3) account for a very low number frequency (0.3%), and complex shape. The present study addresses the local stress/strain behavior in a cast-pore containing HPDC AM60 sample during tensile loading investigated using 3D image-based models which consider the actual size, morphology, and spatial distribution of pores based on XRT images and consider the actual material properties of the AM60 alloy. Simulation results show that the local stress/strain around a pore evolves progressively with deformation. The strain at a certain pore location may be amplified or reduced in the presence of other pores, depending on the specific location of the concerning pores. Also, the ratio between the projected area of a pore and its shortest distance to the free surface (PA/SD) could give a good indication of the max local stress concentration around the pore surface. The weakening of Ktpl values of pores found in defect bands are principally due to the pore orientation concerning the load direction. These findings may be extended to provide additional insight into the damage mechanisms in material containing casting pores and to enhance understanding of the ductility variation in terms of local deformation fields around pores and their interactions.
Aluminium composites have been extensively developed for automotive applications due to their high specific strength. However, particle agglomeration, high porosity content, and weak ...reinforcement/matrix interface bond are prone to occur in the casting process. These arise during the introduction of the reinforcement, mould filling, and solidification process, especially when the particle sizes are approaching the nanoscale and are detrimental, with respect to the mechanical properties. By applying high pressure in conjunction with high cooling rates, an improved distribution of the reinforcing particles can be expected, as the high pressure improves the filling capacity of the composite melt, in which the fluidity is generally decreased by the added heterogeneous particles. The fine grain structure obtained under the high cooling rate is also beneficial for the distribution of the reinforcing nanoparticles during solidification. In this study, SiC nano-reinforced AlSi9Cu3 composites were developed by employing an Al–Cu-SiCnp master alloy, stir mixing, ultrasonication and HPDC technology. The findings showed a good distribution of individual SiC particles, resulting in a reduction of ∼40% in the α-Al grain size and near 10% increment in the yield strength, which was attributed to grain refinement, CTE strengthening and Orowan strengthening. Compared to commercial AlSi9Cu3 HPDC alloys, the developed AlSi9Cu3-1wt% SiCnp composite provided an improved YS of ∼187 MPa and a UTS of ∼350 MPa in the as-cast state and the milestone high YS and UTS of ∼370 MPa and ∼468 MPa under a T6 condition, respectively.
•CAE simulation had been conducted to optimize the gate and runner design of an automobile part.•By comparing the filling process of other casting layouts, the optimal layout design had been ...founded.•The pivoting block on the runner center seems to be useful concept to prevent any generated backflows.•The shrinkage defect areas had been observed with the modulus method on the solidification process. The heat-shrink is occurred on those areas due to ununiformed cooling temperature and causes the shrinkage defects from our past tooling experiments.
A most important progress in civilization was the introduction of mass production. HPDC molds are one of main technologies for mass production. Due to the high velocity of the liquid metal, aluminum die-casting is so complex where flow momentum is critical matter in the mold filling process. Actually in complex parts, it is almost impossible to calculate the exact mold filling performance with using experimental knowledge. Due to this condition in the design procedure, the simulation is becoming more important. Simulation can make a casting system optimal and also elevate the casting quality with less experiment. The most advantage of using simulation programs is the time and cost saving of the casting layout design. The condition selection of HPDC mainly relied on the experience and expertise of an individual worker in casting industries. Systematic knowledge accumulation of die casting process was an essential matter to get optimal process conditions.
In present casting industries, product development paradigm is shifting from traditional trial-and-error to proof-of-concept based on CAE -enabled simulation. Due to the high velocity of the dynamic behavior of the casting system in working conditions, aluminum die casting is a very complex process in which flow momentum is a critical issue in the mold filling process. In the new production development paradigm, CAE simulation plays an important role because it models the entire casting process and reveals the dynamic behavior of the casting system. In this research, CAE simulation was performed by using the simulation software (AnyCasting) in order to optimize the gate and runner design of an automobile part (Oil Pan_BR2E) which is well known and complicated to achieve a good casting layout. Filling analysis was used to find out the size and location of the gate and proper runner system design. By the modification of the gate and runner system and the configuration of overflows, internal porosities caused by air entrapments were predicted and reduced remarkably. With the solidification analysis, internal porosities caused by the solidification shrinkage were also predicted.
Different weight ratios of cerium (0.5, 1 and 2 wt.%) were produced in a controlled atmosphere by High Pressure Die Cast method to Mg-6Al-0.3Mn-1Sn alloy. The influence of cerium on microstructure ...and high-temperature mechanical properties was investigated. The microstructure study revealed that the main alloy contains intermetallic phases such as α-Mg, β- Mg
17
Al
12
, Mg
2
Sn and Al
11
Ce
3
. The hardness values of the alloys were increased with the addition of 0.5%, 1 and 2 cerium. With the addition of 0.5 wt.% Ce, the yield strength increased to 145 MPa. With the addition of 2 wt.% of Ce, it was found to be 160 MPa with an increase of 14%. Tensile strength was obtained as 190 MPa. Elevated temperature tensile test was carried out at 120°C, 180°C and 240°C, to all the alloys. It was found that increased Ce ratio increased the high-temperature mechanical strength. At 120°C, the highest tensile and yield strength values were obtained with 159 MPa and 147 MPa, respectively, in the alloy with 2% wt. cerium added. In the tensile test performed at 180°C, the highest tensile and yield strength were measured as 91 MPa and 77 MPa, respectively. The operating temperature of Mg alloys produced industrially by HPDC has a significant effect on mechanical properties. High operating temperatures reduce mechanical properties. However, the mechanical properties at high test temperatures were increased by the addition of Ce metal to the AM60-1Sn-XCe alloy produced with HPDC.
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