Al–Si–Mg based alloys can provide high strength and ductility to satisfy the increasing demands of thin wall castings for automotive applications. This study has investigated the effects of T6 heat-treatment on the microstructures, the local mechanical properties of alloy phases and the fracture behavior of high vacuum die-cast AlSiMgMn alloys using in-situ scanning electron microscopy (SEM) in combination with nano-indentation testing. The microstructures of the alloys at as-cast and T6 treated conditions were compared and analyzed. It is found that the T6 heat treatment plays different roles in affecting the hardness and the Young’s modulus of alloy phases. This study also found that the T6 heat treatment would influence the failure modes of the alloys. The mechanisms of crack propagation in the as-cast and T6 treated alloys were also analyzed and discussed.

Nanoscale manufacturing imposes demands on prediction of cutting processes on small scales. Predictive modeling schemes based on the underlying physical mechanisms could potentially be more generally applicable in manufacturing. In this work, the experimental and numerical studies on polymethyl methacrylate (PMMA) nanocutting are reported. The cutting experiments were performed on an ultramicrotome instrumented with piezoelectric transducers to measure the cutting forces on cutting down to about 60 nm thickness. Using atomic force microscopy, the surface damage was identified as shear yield bands triggered by adiabatic heating. A suitable physical model including these observed phenomena made it possible to link the processing conditions with the onset of damage, i.e., the transition between a high-quality transparent surface and a damaged uneven surface. Finite element analysis was carried out to investigate the deformation modes of PMMA under different cutting conditions and to predict the formation of the undesired shear bands. From an engineering perspective, such an approach could be potentially useful in improving manufacturing control.

In this study, an innovative modeling approach has been proposed to demonstrate the removal mechanisms of Polymethyl Methacrylate (PMMA) reinforced with randomly distributed carbon nanotubes (CNTs) during nanosectioning. The viscoplastic behavior of the matrix polymer was described using the Mulliken–Boyce model and the distribution of the CNTs in the matrix was modeled using the random sequential adsorption (RSA) method. The effects of cutting thickness and CNT loading on the machinability of the nanocomposites are explored. Subsequent experiments were conducted to validate the modeling. It reveals that the addition of CNT increases the resistance to cutting, compared to the malleable matrix. Although the primary strain distribution for both plain PMMA and PMMA/CNT composites aligns closely, discernible disparities between the two materials emerge. A force augmentation is anticipated whenever a nanotube interacts with the cutting tool, which causes surface protrusions and sub-surface damage. The addition of CNT with a loading lower than 1.0 wt% does not change the mechanisms of chip formation, but the addition of 1.0 wt% CNTs increases cutting force by approximately 32%. This work provides a feasible approach and framework to numerically model the nanosectioning of CNT-reinforced thermoplastics.

The morphology of porosity formed during laser-based thermal joining of thermoplastics and metals has not been understood well and causes considerable uncertainty in the design and manufacturing of hybrid structures. In this work, high-resolution X-ray computed tomography (μ-CT) was used to analyse the porosities inside polycarbonate (PC) and glass fibre reinforced polycarbonate (GFRPC) welded with DP590 steel using a laser, and the quantitative characteristics of the morphology and distribution of the porosities were extracted. Significant differences were found between the two types of laser joints. For the DP590/PC joints, below a critical line energy (LE), the load-bearing capacity of the joint increased with increasing LE, above which it maintained nearly constant. The maximum tensile strength equivalent to approx. 75% of the tensile strength of the bulk PC was achieved. The load-bearing capacity for the DP590/GFRPC joints was much lower than that of the DP590/PC joints. The DP590/PC joints had a large number of round porosities caused by polymer pyrolysis. In contrast, the DP590/30%GFRPC joints had more irregular porosities caused by shrinkage. A transient thermal conduction model was developed to predict the temperature field during laser joining. The predicted melting region was then correlated with the porosity distribution characterized by μ-CT. The spatial distribution of the porosities was found to match the predicted region of resin melting in the modelling closely.