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Alloy wheels must meet rigorous durability and safety tests to meet structural demand during use. The use of aluminum (Al) alloyed with silicon (Si) stands out due to the good relationship between density and strength and also its esthetic appeal, which is made possible by the suitable alloy machinability. The use of A356 alloy processed through low-pressure die casting and T6 heat treatment comes from the need for suitable mechanical properties and ease of large-scale cyclic processing. The wheel sector's high competitiveness demands accelerated development with less time-to-market and better performance. The use of numerical cast simulations helps predict the thermal and microstructural parameters of the alloy resulting from the solidification process inside a metallic mold. Understanding the solidification thermal parameters is of great importance for predicting either the phase morphologies or the dendritic length-scale of the casting, since these features have a direct impact on the alloy's strength. The present study aims to develop a computational simulation tool using commercial casting software to predict the tensile properties of as-cast and heat-treated automotive wheels. To achieve this objective, directional solidification (DS) experiments with the A356 alloy were carried out in order to determine equations relating the solidification time and cooling rate along the casting. The generated casting by the DS was further divided into parts, heat-treated and untreated, and each half part was examined for both tensile testing and the determination of secondary dendrite arm spacing (λ2). This allowed the development of key experimental equations relating λ2 with solidification time and tensile properties with λ2. In the end, a coupled simulation tool underwent testing using real tensile test data from wheels before and after T6 treatment. This testing involved two methods of correlating tensile properties with λ2: Hall-Petch-type (HP) and Ludvig model approaches. The HP model more accurately represents the strength data from various wheel regions, with a small average error of approximately 5.6% for ultimate strength. [ABSTRACT FROM AUTHOR]

The Indian foundry industries are facing problems to produce the casting at a lower cost due to an increase in the cost of the raw materials. On the other hand, the use of Fe–Cr slag as a mold material in foundry industries was not explored. Therefore, the present investigation was focused on the designing and optimization of Fe–Cr slag mold's constituents for Al-alloy (A356) castings. The optimum properties of the Fe–Cr mold such as mold hardness number, permeability number, compressive, and shear strength were found to be 87, 158, 1.45 kg/cm2, and 0.38 kg/cm2, respectively. Aluminum alloy (A356) castings were made from Fe–Cr slag and silica sand mold. It was observed that Fe–Cr slag mold casting has good dimensional stability in comparison to silica sand mold casting. The Brinell hardness and microstructure of the castings were evaluated and a possible structure-property relationship was explained. It was observed that Fe–Cr slag has a lot of potentials to be used as an alternative to silica sand mold for Al-alloy castings. However, its recyclability, production of required particle size of Fe–Cr slag using atomization, and its cost need to be studied before recommending its use in Indian foundry industries. [ABSTRACT FROM AUTHOR]

Mechanical properties of the castings are directly affected negatively by the inclusions, such as its own oxide occurring during melting, if proper and logical liquid metal processes could not be carried out. To overcome this issue, different compositions and types of fluxes were practiced. Na2SiF6, NaF/AlF3 (cryolite ratio) = 1.85, 2.8, and 3, NaF, Na3AlF6 (commercial cryolite) added with different ratios to the mixture of NaCl+KCl, and also only Na2SiF6 to the mixture of MgCl2+KCl were appended to the liquid metal to remove inclusions, such as old oxide bifilms. Average effectiveness values of the fluxes concerning mechanical properties were investigated as well. The change in the melt cleanliness before and after degassing has been taken into account to establish a model that correlates bifilm index and tensile properties. Since bifilm index is directly interested in porosity shape and amount to quantify liquid metal quality, any other techniques, such as density index, were not be consulted. In addition, the main focus was based on how much the melt was cleaned rather than the cleanliness of the melt after degassing. Thus, the difference of bifilm index as a melt cleanliness indicator firstly was introduced to the literature. In addition to this, the contour plots of mechanical properties and bifilm index values were used to evaluate the correlation, and it was found that there was an exponential relationship, a quality index, between elongation at fracture, tensile strength, and bifilm index. [ABSTRACT FROM AUTHOR]

The present investigation was focused on designing and developing Narmada riverbed sand (NRS) as an alternative to commercial-grade silica sand (CGSS) for the green sand mold casting process. The green NRS mold constituents were modeled and optimized through response surface methodology (RSM) to achieve the mold's desired physical and mechanical properties. The RSM model predicted the optimum constituents of NRS mold and found it to be 4.4 wt% moisture, 11.7 wt% bentonite, and 3.9 wt% coal dust to achieve the desired mold properties. The properties of NRS mold, such as mold hardness, permeability number, compressive strength, and shear strength, were found to be 88, 209, 1.6 kg/cm2 (0.156 MPa), and 0.38 kg/cm2 (0.037 MPa), respectively. A laboratory trial of aluminum-silicon alloy (A356) cuboid casting was conducted using green NRS and CGSS mold. The as-cast dimensions, surface roughness, hardness, and microstructure were evaluated and compared. It is observed that the NRS mold is suitable for A356 alloy casting. However, the recyclability of Narmada riverbed sand may be studied further to understand its commercial use as an alternative material to CGSS for non-ferrous alloy casting in Indian foundries. [ABSTRACT FROM AUTHOR]

The present investigation focuses on the development of metal casting mold using stone-dust as an alternative mold material to silica sand. The stone-dust aggregate mold having 4 wt.% of moisture and 11 wt.% of bentonite clay shows desired mold properties as per AFS standard. The mold properties such as permeability number, hardness (B-scale), compressive, and shear strength are 147, 88, 1.48, and 0.33 kgf/cm2, respectively. The fusion point of stone-dust is found to be below 1350 °C and phase changes are observed above 1000 °C. Hence, the stone-dust mold is suitable for Al alloy casting. Therefore, a laboratory-scale casting trial is taken to cast A356 alloy using green stone-dust and silica sand mold. The hardness (HRB), as cast surface roughness (Ra) and microstructure of silica sand and stone-dust mold casting are evaluated and compared. It is observed that stone-dust mold shows higher hardness as compared to silica sand mold. Hence, stone dust mold may be used as an alternative to silica sand in Indian foundries for aluminum alloys casting. [ABSTRACT FROM AUTHOR]

Anticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3). [ABSTRACT FROM AUTHOR]

Permanent mold metal casting processes use tempering with oil, water or air as state-of-the-art method for temperature control of certain regions. This approach aims at either creating certain temperature gradients inside the die thus leading to better casting quality or cools down critical hotspots in order to decrease cycle times or increase service life. In order to perform an investigation on the influences of oil tempering on a permanent die and the solidification of the aluminum alloy A356, an experimental setup is used with measurement instrumentation for recording temperatures inside the melt and die as well as recording the movement of the die and the casting, thus enabling a gap width determination and measuring the contact pressure present on an inner core. A thermomechanical simulation of the solidification also is performed representing the processes occurring inside the experimental setup and extending the available data beyond the information locally provided at the experimental measuring positions. This approach allows for an evaluation of the influence of oil tempering on the solidification process, the thermal conditions inside of the casting, die, and core, and describes the behavior of a one-sided cooling of a comparatively large melt volume as well as the influences on a region with two-sided heat extraction affecting a smaller melt volume. [ABSTRACT FROM AUTHOR]

In this study, the cooling behavior of Sr-modified A356 alloy aluminum wheels produced by low-pressure die-casting technology was investigated in different quenching mediums. Water and surfactant quenchants were used in order to determine the cooling rate and mechanical properties of the alloy. A thermocouple was attached to the wheels, and parts were immersed into different quenching mediums after solution treatment. Data were collected by using a data logger. Tensile test and hardness test were carried out in order to determine the effect of quenching step on mechanical properties. Statistical analysis was performed, and graphics were drawn with Minitab. Maximum cooling rates throughout the quenching were obtained, respectively, 61–68–70–85 °C/s at SDS, Triton X-100, Tween 20 and water quenching medium. It was found that 61 °C/s is enough to suppress precipitation for artificially aging, and the cooling rate at Leidenfrost point is the most important parameter for correlation with mechanical properties. According to the hypothesis analysis, only yield strength values were affected by the quenching rate at LDP statistically. [ABSTRACT FROM AUTHOR]

The oxide layer on liquid aluminum serves as a protective property to prevent the alloy from further oxidation. However, it has the potential to be a source of porosity when entrained into the bulk of the liquid. For this reason, oxides entrained into aluminum castings have been shown to degrade casting quality. In the current study, the effectiveness of the reduced pressure test in assessing the quality of A356 alloy melts has been investigated under various conditions obtained by changing six different melt parameters. Several metrics, including average pore size, number density of pores, bifilm index, have been used to measure melt quality. Results have shown that the bifilm index provides reliable measurements of melt quality. Moreover, the bifilm index has been found to have a physical meaning, volume fraction of pores, especially when bifilm index is higher than 50 mm. [ABSTRACT FROM AUTHOR]

Several models predicting microshrinkage in castings are revised in this analysis. A mathematical model, based on Niyama criterion, is introduced here which considers the stochastic behavior of pore nucleation during casting solidification. For this model, literature validation is provided for an A356 alloy plate casting. Further validation is provided for a bar geometry cast in a silica sand mold. The model predictions match reasonably well with the experimental pore percentage profile. [ABSTRACT FROM AUTHOR]