A И-Shaped Curve of Hot Tearing Susceptibility in Magsimal®-59-Based Alloys

The hot tearing susceptibility of Al-6Mg-xSi (x = 0-6.0 wt.%) alloys was studied using constrained rod casting. Addition of Si content resulted in double ternary eutectic reactions and then changed the freezing range and eutectic liquid fraction greatly, which made the hot tearing susceptibility show a И-curve with the increasing of Si content. The И-curve was obviously different from the λ-curve that supported by most researchers.

Effect of Sc on the Hot Cracking Properties of 7xxx Aluminum Alloy and the Microstructure of Squeeze Castings

In this paper, the effect of adding the refiner Sc to the high Zn/Mg ratio 7xxx series aluminum alloy melt on the hot tearing performance, microstructure, and mechanical properties of the alloy is studied. The hot tearing performance test (CRC) method is used to evaluate the hot tearing performance of the alloy. The squeeze casting process was used to form solid cylindrical parts to analyze the structure and properties of the alloy. This study shows that the hot cracking sensitivity of the alloy after the addition of the refiner Sc is significantly reduced. The ingot grain size is significantly reduced, and the average grain size is reduced from about 86 μm to about 53 μm. While the mechanical properties are significantly improved, and the tensile strength reduced from 552 MPa is increased to 571 MPa, and the elongation rate is increased from 11% to 14%.

A spectrum-domain instance segmentation model for casting defects

Accurate segmentation of casting defects plays a positive role in the quality control of casting products, and is of great significance for accurate extraction of the mechanical properties of defects in the casting solidification process. However, as the shape of casting defects is complex and irregular, it is challenging to segment casting defects by existing segmentation methods. To address this, a spectrum domain instance segmentation model (SISN) is proposed for segmenting five types of casting defects with complex shapes accurately. The five defects are inclusion, shrinkage, hot tearing, cold tearing and micro pore. The proposed model consists of three sub-models: the spectrum domain region proposal model (SRPN), spectrum domain region of interest alignment model (SRoIAlign) and spectrum domain instance generation model (SIGN). SRPN uses a multi-scale anchoring mechanism to detect defects of various sizes, where the SSReLU and SCPool functions are used to solve the spectrum domain gradient explosion problem and the spectrum domain over-fitting problem. SRoIAlign uses the floating-point quantization operation and the tri-linear interpolation method to quantize the 3D proposals to the feature values in an accurate manner. SIGN is a full-spectrum domain neural network applied to 3D proposals, generating a segmentation instance of defects in a point-wise manner. In the experiments, we test the effectiveness of the proposed model from three aspects: segmentation accuracy, time performance and mechanical property extraction accuracy.

Additive manufacturing of aluminium alloy 2024 by laser powder bed fusion: microstructural evolution, defects and mechanical properties

Purpose The purpose of this study is to investigate the microstructural evolution of high-strength 2024 Al alloy prepared by the laser powder bed fusion (L-PBF) additive manufacturing (AM) route. The high-strength wrought Al alloy has typically been unsuitable for AM due to its particular solidification characteristics such as hot cracking, porosity and columnar grain growth. Design/methodology/approach In this research work, samples were fabricated using L-PBF under various laser energy densities by varying laser power and scan speed. The microstructural features that developed during the solidification are correlated with operating laser parameters. In addition, finite element modelling (FEM) was performed to understand the experimentally observed results. Findings Microstructure evolution and defect formation have been assessed, quantified and correlated with operating laser parameters. Thermal behaviour of samples was predicted using FEM to support experimental observations. An optimised combination of intermediate laser power and scan speed produced the least defects. Higher energy density increased hot tearing along the columnar grain boundaries, while lower energy density promoted void formation. From the quantitative results, it is evident that with increasing energy density, both the top surface and side wall roughness initially reduced till a minimum and then increased. Hardness and compressive strength were found to decrease with increasing power density due to stress relaxation from hot tearing. Originality/value This research work examined how L-PBF processing conditions influence the microstructure, defects, surface roughness and mechanical properties. The results indicates that complete elimination of solidification cracks can be only achieved by combining process optimisation and possible grain refining strategies.