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Most aluminum cylinder blocks produced using high-pressure or low-pressure die-casting processes require gray cast iron liners (GCI liners) to compensate for their insufficient wear resistance and heat resistance of the Al-Si-Cu alloys. However, the cast-in liners cause excessive residual stress at the cylinder bore region. The resultant residual stress induces distortion of the cylinder liner. These inconveniences hinder development of more efficient engines. Therefore, an accurate thermal stress analysis technique has been sought to predict the residual stress and distortion of the cylinder liner. For accurate thermal stress analysis, we have already developed an elastoplastic-creep constitutive equation for which the inelastic strain developed at high temperatures does not contribute to strain hardening that occurs at low temperatures by duplicating the recovery behavior. Our earlier investigation using this equation has already revealed that incorporation of the recovery in the alloy constitutive equation is effective for improving the prediction accuracy of the thermal stress developed during casting. However, this conclusion was obtained only for a simple shape casting with a uniaxial thermal stress state. Effects of the developed constitutive equation have not been discussed for a casting closer to an actual cylinder block. For this study, a cylindrical aluminum casting with GCI (ISO 300) insert was produced. Then, the circumferential strain of the GCI liner was measured in-situ during casting. Measurements were taken of the residual stresses of the cylindrical aluminum casting and GCI liner, and of the liner deformation at a room temperature. The experimentally obtained results supported a discussion of the predictive accuracies of the elastoplastic-creep constitutive equation and the classical elastoplastic constitutive equation. A comparison revealed that the elastoplastic-creep constitutive equation for the aluminum casting has better predictive accuracy than the classical elastoplastic equation for residual stress, liner deformation, and the circumferential strain of a GCI liner during casting. Investigation of the simulated strain components of the cylindrical aluminum casting during casting indicated incorporation of the recovery in the alloy constitutive equation as a main factor improving the predictive accuracy. [ABSTRACT FROM AUTHOR]

Recovery behavior (recovery) and strain-rate dependence of the stress-strain curve (strain-rate dependence) are incorporated into constitutive equations of alloys to predict residual stress and thermal stress during casting. Nevertheless, few studies have systematically investigated the effects of these metallurgical phenomena on the prediction accuracy of thermal stress in a casting. This study compares the thermal stress analysis results with in situ thermal stress measurement results of an Al-Si-Cu specimen during casting. The results underscore the importance for the alloy constitutive equation of incorporating strain-rate dependence to predict thermal stress that develops at high temperatures where the alloy shows strong strain-rate dependence of the stress-strain curve. However, the prediction accuracy of the thermal stress developed at low temperatures did not improve by considering the strain-rate dependence. Incorporating recovery into the constitutive equation improved the accuracy of the simulated thermal stress at low temperatures. Results of comparison implied that the constitutive equation should include strain-rate dependence to simulate defects that develop from thermal stress at high temperatures, such as hot tearing and hot cracking. Recovery should be incorporated into the alloy constitutive equation to predict the casting residual stress and deformation caused by the thermal stress developed mainly in the low temperature range. [ABSTRACT FROM AUTHOR]

Accurate simulation of residual stress and deformation is necessary to optimize the design and lifetime of casting components. Therefore, the recovery and strain-rate dependence of the stress-strain curve have been incorporated into empirical constitutive equations to improve the thermal stress analysis accuracy. Nevertheless, these equations present several difficulties related to the determination of material constants and their physical bases. This study suggested an empirical elasto-plastic-creep constitutive equation incorporating these phenomena. To determine the material parameters used in this constitutive equation, this study investigated tensile test methods to obtain stress-strain curves that most closely resemble those during or immediately after casting for the Al-Si-Cu high-pressure die-casting alloy JIS ADC 12 (A383.0), which exhibits natural aging. Results show that solution heat treatment with subsequent cooling to the test temperature should be applied to obtain stress-strain curves used for the thermal stress analysis of high-pressure die casting process of this alloy. The yield stresses obtained using the conventional heating method were 50-64 pct higher than those of the method described above. Therefore, the conventional method is expected to overestimate the overestimation of the predicted residual stress in die castings. Evaluation of the developed equation revealed that it can represent alloy recovery and strain-rate dependence. [ABSTRACT FROM AUTHOR]

Non-heat-treated Al–Mg-based die casting alloys have been developed for the structural parts of automobiles. In previous studies, alloy compositions with at least 1.0%Si have been proposed to reduce the hot tearing susceptibility (HTS). On the other hand, the increase in the Si content reduces the ductility. For some automotive body structures, Al–Mg alloy die castings with Si content exceeding 1.0% should not have the required ductility. This study aims to develop an Al–Mg alloy with both high ductility and low HTS by investigating the following three characteristics of an Al–4.5Mg–1.0Mn alloy with 0.2%Si added: (1) additional elements to reduce the HTS, (2) the associated mechanical properties (requirements for the automotive company: 0.2% proof stress ≥ 140 MPa and fracture elongation ≥ 15%), and (3) the mechanism of decreasing the HTS. It was revealed that the co-addition of 0.025%Sr, 0.08%Ti, and 0.016%B reduced the HTS when the hydrogen content of the melt was 0.5–1.0 mL/100 g Al. Furthermore, the 0.2% proof stress and fracture elongation of a lower link arm produced via HPDC with the above composition were found to achieve the requirements. It was also indicated that the mechanism of decrease in the HTS by the Sr addition should result from the decrease in the thermal tensile load due to the formation of hydrogen porosity at a lower solid fraction than that without Sr. It is suggested that when 0.025%Sr, 0.08%Ti, and 0.016%B are added to the Al–4.5Mg–1.0Mn–0.2Si alloy, non-heat-treated automotive structural parts with both high ductility and low HTS will be obtained by high-pressure die casting. [ABSTRACT FROM AUTHOR]