面向选区激光熔化薄壁悬垂结构的自适应工艺优化研究

近年来，通过选区激光熔化（Selective Laser Melting，SLM）技术制造Ti6Al4V合金部件在航空航天、军事和医疗领域的应用越来越多。SLM技术的高自由度和几何精度为薄壁悬垂零件的制造开辟了新的途径。然而，由于薄壁悬垂结构的悬空特性，使得在SLM过程中悬垂边缘位于粉末支撑区域，从而导致了较高的表面粗糙度以及较低的纳米硬度，严重阻碍了该技术的发展。本课题利用SLM技术制造薄壁悬垂样件，深入探究了工艺参数以及悬垂角对薄壁悬垂结构表面形貌、物相组成、微观组织和致密度的影响；揭示了工艺参数、悬垂角与表面粗糙度、纳米硬度间的映射关系；建立了工艺自适应优化方法，以同时优化悬垂结构上、下斜面的粗糙度和纳米硬度。

针对悬垂斜面粗糙度较差的问题，系统研究了工艺参数和悬垂角对悬垂结构上、下斜面表面形貌的影响。结果表明，悬垂结构上、下斜面的表面形貌存在显著差异且上斜面粗糙度通常低于下斜面。下斜面粗糙度随悬垂角减小、激光功率增加而增大，随扫描速度的增加呈现先增加后减小的趋势。而上斜面粗糙度则几乎不受悬垂角影响，与线能量密度呈正相关趋势。随后，使用双调和样条插值（V4）法生成响应面模型，旨在同时改善上、下斜面的粗糙度，优化方法可使上、下斜面的粗糙度同时降低约50%。

针对悬垂结构纳米硬度较低的问题，分别研究了悬垂角和激光功率对物相组成、微观组织和致密度的影响。结果表明，较小的悬垂角会提高Al和V在α΄-Ti基体中的固溶度，且会使柱状晶β相不再沿构建方向生长成直条状而是形成不规则形状，致密度也会由于飞溅、球化现象的加剧而减小。激光功率增加导致了更高的温度梯度和更快的冷却速率，从而降低了成核潜力，致使形成粗壮的β柱状晶并细化了α΄晶粒，致密度也由于孔隙增多而显著下降。因此导致纳米硬度随悬垂角的减小和激光功率的增大而减小。

本课题揭示了工艺参数、悬垂角与性能之间的关系，并且为优化薄壁悬垂零件的粗糙度和硬度提供了重要指导。研究结果对于推动选区激光熔化技术在轻质化悬垂零件制造领域的应用和发展具有重要意义。

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