Selective laser-melted (SLMed) 7075 aluminium alloy is prone to cracking. Erbium (Er) could modify the aluminium alloys to prevent cracking in traditional manufacturing processes. In the present study, Er-modified 7075 aluminium alloy powders are prepared to investigate the influence of Er element on crack reduction in SLM. The evolution of Er is characterised by a scanning electron microscope (SEM), a X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The results show that the crack density is reduced with Er addition, but the porosity increases, a new discovery. Based on the SEM and TEM results, Er addition exists in the form of unmelted particles and Al₃Er of sub-micrometer scale. The Er particles in the molten pool deteriorate the fluidity and result in higher porosity. The coherency between aluminium matrix and Al₃Er favours the grain refinement, therefore the crack reduction.

Two-photon polymerization (TPP) is a sub-classification of vat photopolymerization. It has been widely used to fabricate micro/nano hierarchical structures that have the potential to be used to tune the fluid flow in chips. The present work first studied the influence of laser power on the feature size of TPP-fabricated 2D structures. It was found that the increase of laser power from 1.0 μW to 1.4 μW leads to the feature size increasing from 203 nm to 307 nm. Then, the effect of scanning parameters on the accuracy and surface quality of 3D structures was investigated. The arrangement of the voxels at different scanning strategies explains the mechanisms of the variation of accuracy and surface roughness. Finally, the pinecone structures with micro/nano hierarchical features were built and evaluated for their water repellence. The increase in the number of rows of pinecone structures significantly enhances the water-repellent performance.

The inherent sparsity of LiDAR point cloud data presents a fundamental challenge for 3D object detection. During the feature encoding stage, especially in voxelization, existing methods find it difficult to effectively retain the critical geometric structural information contained in these sparse point clouds, resulting in decreased detection performance. To address this problem, this paper proposes an enhanced 3D object detection framework. It first designs a Structured Voxel Feature Encoder that significantly enhances the initial feature representation through intra-voxel feature refinement and multi-scale neighborhood context aggregation. Second, it constructs a Hybrid-Domain Attention-Guided Sparse Backbone, which introduces a decoupled hybrid attention mechanism and a hierarchical integration strategy to realize dynamic weighting and focusing on key semantic and geometric features. Finally, a Scale-Aggregation Head is proposed to improve the model’s perception and localization capabilities for different-sized objects via multi-level feature pyramid fusion and cross-layer information interaction. Experimental results on the KITTI dataset show that the proposed algorithm increases the mean Average Precision (mAP) by 3.34% compared to the baseline model. Moreover, experiments on a vehicle platform with a lower-resolution LiDAR verify the effectiveness of the proposed method in improving 3D detection accuracy and its generalization ability.

Laser powder bed fusion (LPBF) of high-strength aluminum alloy 7075 (AA7075) is severely limited by hot cracking. However, the underlying mechanisms, particularly the coupling between thermal fields, solidification microstructure, and cracking behavior, remain insufficiently clarified. This study elucidates these mechanisms by integrating experimental characterization with thermal simulation to investigate the temperature field, microstructure, and cracking relationships in both AA7075 and a crack-resistant 7075-Er-Zr alloy. Results show that coarse hot crack morphology is highly dependent on linear energy density E_L. In AA7075, E_L < 450 J/m promotes laterally inclined cracks (short, narrow cracks extending from the melt pool boundary toward the track center), whereas E_L higher than that value leads to the continuous centerline cracks (long, wide cracks along the track center). Fine microcracks are also observed at melt pool boundaries. The 7075-Er-Zr alloy demonstrates superior crack resistance. At E_L = 600 J/m, longitudinal centerline cracks still penetrate along the track, but the alloy achieves crack-free tracks at 200 W with scanning speeds above 1000 mm/s, otherwise exhibiting only short discontinuous cracks. Microcracks at melt pool boundaries are markedly suppressed in the modified alloy. The enhanced crack resistance is attributed to Er/Zr-induced grain refinement and a transition to an equiaxed grain structure, which disrupts intergranular gaps. Critically, thermal simulations identify an annular region with a peak temperature gradient. In AA7075, this region develops aligned columnar grains that facilitate both microcracks and centerline cracks. In the 7075-Er-Zr alloy, microcracks are fully eliminated within this region. However, a residual crystallographic texture persists in the annular region, which promotes the continued occurrence of centerline cracks under high energy density (e.g., E_L = 600 J/m). The annular region remains a critical weak link, and its microstructural control determines the prevailing crack type. This work provides a fundamental understanding of the thermal-microstructural origins of cracking and offers a theoretical foundation for developing crack-resistant aluminum alloys via LPBF.