AM60B镁合金激光熔凝工艺研究

采用横流CO2激光器,对AM60B镁合金进行激光熔凝处理,同时改变激光加工工艺参数,得到不同的熔凝组织.讨论了各工艺参数对熔凝区尺寸的影响规律,并分析了熔凝区组织性能之间的关系.结果表明,激光熔凝后,晶粒得到细化,硬度提高约50％,耐磨性提高约60％.     

镁合金激光表面熔凝处理研究进展

镁合金是优异的轻量化材料和极具潜力的人体植入材料,但其耐蚀性差。激光表面熔凝技术可快速在镁合金表面形成晶粒细小的熔凝层,改善镁合金表面微观形貌和组织结构,对提高其表面耐蚀性和生物相容性有重要作用。综述了近年来镁合金激光表面熔凝处理的相关研究工作,分析了熔凝处理工艺对镁合金微观结构、成分、润湿性、耐蚀性和生物相容性的影响。总结并展望了激光熔凝处理在镁合金的组织结构转变、腐蚀机理及力学行为、降解行为和生物相容性等方面的发展方向。     

铝硅合金激光熔凝强化及其机制

本文研究了共晶铝硅合金激光熔凝强化的机理，特别是利用了人工时效使其复合的强化作用得到分解，研究结果表明：这种强化是以细晶强化为主，以固溶强化为辅，伴有少量第二相强化的工艺。这种强化可以使硬度及耐磨性提高一倍左右。     

镁合金的激光表面处理技术

评述了激光表面熔凝、激光表面合金化和激光表面熔覆技术用于镁合金表面处理中提高其耐蚀性和耐磨性的机制,以及这些表面处理技术的研究现状。并探讨了激光表面处理技术在镁合金应用中存在的问题和该技术的发展前景。     

激光模具表面非熔凝加工的应用研究

通过建立试件的热分析模型,对激光模具表面非溶凝加工过程进行了有限元分析,从而对激光相为硬化过程中的温度场、残余热应力、应变场进行了研究。通过计算机模拟,获得指导性工艺参数,并对式件进行激光强化试验,将计算值与试验值进行耦合,从而获得最佳工艺参数,提高模具的使用寿命。     

镁合金激光表面处理技术的应用

激光加工技术是近几十年来迅速发展起来的一门高新技术.综述了激光表面改性技术在镁合金上的研究与应用.探讨了激光表面处理技术在镁合金中应用的发展趋势和广阔前景.     

固溶冷却方式对AM50镁合金组织和耐蚀性能的影响

通过XRD、SEM、EDS、电化学腐蚀测试,研究了铸造AM50镁合金固溶后水冷和炉冷两种处理方式对组织及耐蚀性能的影响。结果表明,固溶处理后,由于大量Al固溶进α-Mg中,两种方式冷却的AM50镁合金相组成主要为α-Mg、Al₆Mn和少量β-Mg₁₇Al₁₂。由于冷却速率的不同,炉冷样比水冷样的β-Mg₁₇Al₁₂的数量多,体积大,并且围绕Al₆Mn相析出,而且大多在晶界处析出。由极化曲线和腐蚀速率曲线可以看出炉冷样的腐蚀速率较高,耐蚀性较差。由于β-Mg₁₇Al₁₂数量的增加以及α-Mg相中固溶Al的数量减少,导致炉冷试样比水冷试样的腐蚀速率高,而且经过168 h腐蚀形成了蚀坑带。     

扫描速度对镁合金激光熔凝层组织及性能的影响

采用500 W脉冲激光器以不同扫描速度在AZ91D镁合金表面进行激光熔凝,运用XRD、SEM、EDS等手段测试了熔凝层的组织、显微硬度、耐磨性、耐腐蚀性等。结果表明,激光熔凝能提高镁合金的表面硬度及耐磨性,但未能提高其耐蚀性能。激光扫描速度对熔凝层的硬度影响不大。     

激光在镁合金表面处理中的应用

综述了激光在镁合金表面处理中的应用现状。诸多实验表明,激光表面熔凝、合金化以及激光熔覆都可提高镁合金的硬度、耐摩擦和耐腐蚀等表面性能。镁合金激光表面处理技术具有宽广的应用前景。     

AZ80镁合金激光冲击表面改性

采用预固溶或预时效+LSP形变+后时效处理方法,研究预固溶或预时效以及后时效处理对激光冲击AZ80镁合金组织参数(孪晶和析出相)的影响。结果表明:预固溶+激光冲击强化(LSP)形变处理使LSP强化层内产生高密度孪晶的形变带,离冲击表面越近,孪晶密度越高;经(170℃,16 h)时效处理后,由于残余压应力热稳定性,预固溶+LSP形变强化层仍产生具有高密度孪晶的形变带;同时,弥散析出大量的颗粒状β-Mg_(17)Al_(12)相,优先在应力集中的形变带、孪晶界面和孪晶片层内析出;预时效析出的高密度β相极大地降低冲击强化层孪生产生率,孪晶体积分数明显降低,这是由于LSP诱导的高密度位错和析出相引起的。     

Effect of laser surface melting on friction and wear behavior of AM50 magnesium alloy

In the present study, an attempt has been made to enhance tribological properties of AM50 magnesium alloy by laser surface melting (LSM) with a 2 kW continuous wave CO₂ laser. The microstructure of the laser surface melted zone consists of fine columnar dendrites growing epitaxially from the liquid-solid interface. Microhardness of the melted zone was improved to 55-75 HV as compared to 40 HV of the substrate. The friction and wear behavior of the laser surface melted layer were investigated using a ball-on-flat apparatus under dry sliding condition. It was found that the friction coefficient curve of the laser surface melted layer was similar to that of substrate. They showed a lower initial friction coefficient about 0.18 that after the running-in period increased up to about 0.38. Furthermore, compared with the AM50 substrate, the wear volume of the laser surface melted layer was decreased by 42%, the wear resistance of the laser surface melted layer was improved.     

Corrosion of friction stir welded magnesium alloy AM50

The microstructure of a friction stir welded magnesium alloy AM50 was examined by means of optical light microscopy. The chemical composition, particularly the iron content, and morphology of the oxide film were analyzed and discerned via auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Corrosion behaviour of the welds and base materials were investigated by virtue of neutral salt spray tests and potentiodynamic polarization measurements in conventional cells and in a mini cell. The results demonstrate that minor increases in iron concentration as might be speculated to occur as a consequence of tool/work piece interaction during the welding process on the corrosion resistance of the weld can be ignored. The corrosion morphology was predominantly influenced by the distribution of the Mg₁₇Al₁₂ phase. Here, it was also found that the corrosion resistance of the friction stir weld varied in response to changes in the joint microstructure.     

Corrosion behavior of laser melted AZ91HP magnesium alloy

AZ91HP magnesium alloy was melted by CO₂ laser. Compared with as‐received Mg alloy, the grain of the melted layer was refined significantly and the content of Al was increased. The corrosion resistance of the melted layer was improved because of the grain refinement, the redistribution of β‐Mg₁₇Al₁₂ and the increasing of the Al content. As compared to the non‐overlapping zone, the overlapping zone of the melted layer was liable to be corroded.     

Study on microstructure and properties of laser surface melted layer of AZ31B magnesium alloy

An attempt has been made to improve the surface properties of AZ31B magnesium alloy through solid solution hardening and refinement of microstructures using a CO_2 laser as a heat generating source. X-ray diffraction (XRD) was used to identify the phases. Microstructure and properties of laser melted layer of AZ31B magnesium alloy were observed or tested by means of optical microscope (OM), scanning electron microscope (SEM), micro-hardness equipment and electrochemical corrosion equipment etc. The results show that the microstructure of laser melted layer becomes finer significantly and uniform. Compared with the substrate, the content of β-Mg_(17)Al_(12) phase of melted layer decreases comparatively. Microhardness of the laser melted layer is improved to 50-95HV_(0.05) as compared to 40-45HV_(0.05) of the AZ31B Mg alloy substrate. The results of electrochemical corrosion show that the corrosion resistance of laser surface melted layer has been improved.     

Microstructure and tensile properties of squeeze cast magnesium alloy AM50

High-pressure die cast magnesium alloy AM50 is currently used extensively in large and complex shaped thin-wall automotive components. For further expansion of the alloy usage in automobiles, novelmanufacturing processes need to be developed. In this study, squeeze casting of AM50 alloy with a relatively thick cross section was carried out using a hydraulic press with an applied pressure of 70 MPa. Microstructure and mechanical properties of the squeeze cast AM50 with a cross-section thickness of 10 mm were characterized in comparison with the die cast counterpart. The squeeze cast AM50 alloy exhibits virtually no porosity in the microstructure as evaluated by both optical microscopy and the density measurement technique. The results of tensile testing indicate the improved tensile properties, specifically ultimate tensile strength and elongation, for the squeeze cast samples over the conventional high-pressure die cast parts. The analysis of tensile behavior show that the strain-hardening rate during the plastic deformation of the squeeze cast specimens is constantly higher than that of the die cast specimens. The scanning electron microscopy fractography evidently reveals the ductile fracture features of the squeeze cast alloy AM50.     

Microstructure evolution and tensile properties of friction-stir-welded AM50 magnesium alloy

Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties were investigated by using hardness measurement and tensile test,and the fractographs were observed by scanning electron microscopy.The results show that the microstructure of the base material was characterized by bulk primaryαphase,α-matrix and intermetallic compoundβ(or Mg_(17)Al_(12)),and t...     

Corrosion properties of laser surface melted NiTi shape memory alloy

A Nd-YAG laser was used to melt the surface of NiTi shape memory alloy in air and argon environment respectively. The laser surface melted (LSM) layer is free of porosity and crack. The corrosion resistance of the LSM specimen in 3%NaCl solution has been improved significantly and is attributed to the increased amount of TiO₂ and Ti/Ni ratio on the surface.     

激光熔凝处理对NiTi形状记忆合金微动磨损性能的影响

采用高功率连续波固体Nd:YAG激光器,对NiTi形状记忆合金进行激光表面熔凝处理,利用SRVⅢ摩擦磨损试验机考察激光熔凝处理对NiTi形状记忆合金微动磨损性能的影响.采用扫描电子显微镜及能谱仪分析NiTi形状记忆合金表面磨痕形貌及磨损产物成分;用形貌仪测量样品表面磨痕深度,并对磨损体积进行计算.结果表明,与NiTi合金相比,熔凝层摩擦系数,磨损体积均显著降低,表明激光熔凝处理提高了Ni-Ti合金的耐微动磨损性能.NiTi合金微动磨损机理主要表现为氧化和磨粒磨损,而Ni-Ti合金激光熔凝层磨损机制主要以疲劳剥层理论及磨粒磨损为主.     

γ—TiAl基合金的表面激光处理及超塑性扩散连接

较系统地研究了AiAl基合金激光快速熔凝组织细化特征及该类组织的超塑连接规律。结果表明,激光处理后试样表面熔凝区的组织主要为胞状枝晶组织,经后续热处理后转变为细小的等轴晶粒组织,并形成了良好的超塑连接条件。利用该表面组织对试样进行超塑扩散连接,探讨了连接温度,压力和时间对连接效果的影响。表面细化组织试样与整体细化组织试样的超塑连接具有基本相同的连接规律,在连接温度900℃,连接压力60MPa,连接时间1h条件下,可以实现试样的超塑扩散连接。