超声振动对铝合金搅拌摩擦焊焊缝成形的影响

通过超声工具头直接将超声振动施加在搅拌头前方的待焊工件上,在超声振动的条件下对工件进行搅拌摩擦焊,并开展了试验研究,考察了超声振动对6 mm厚6061-T6铝合金平板搅拌摩擦焊焊缝表面成形、截面轮廓、内部缺陷的影响。试验结果表明,施加超声使焊缝表面成形更加光滑美观,接头搅拌区的体积有所增大,在部分工艺参数下能够消除焊缝内部产生的孔洞缺陷。     

Macrostructures and mechanical properties of ultrasonic-assisted friction stir welding joint of 2024-T3 aluminium alloy

In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection of friction stir welding tool and process parameters. Ultimately, such defects degrade the properties of weld and may pose serious concerns towards the integrity and safety of the weld component. In order to improve the properties of weld joints, an ultrasonic-assisted friction stir welding device has been configured where ultrasonic energy is transferred from an ultrasonic unit directly into one of the workpieces near the tool. Using this configuration, ultrasonic-assisted friction stir welding was conducted on 6 mm thick 2024-T3 aluminum alloy sheets. The macrostructure and mechanical properties of these welds were compared with the welds of this alloy prepared by conventional friction stir welding using identical process parameters. The results show that the welding speed can be increased while satisfactory weld quality is still ensured. The ultrasonic energy transferred in this configuration could enlarge the volume of weld nugget zone. Also, the influence of ultrasonic energy on the suppression or elimination of the tunnel defect is quite apparent. However, any beneficial effects of ultrasonic vibration on the tensile strength and the elongation of the joint were less obvious in this configuration.     

超声振动强化搅拌摩擦焊的热力行为及微观组织特征

为了利用超声振动降低搅拌摩擦焊过程中金属材料的屈服应力和流动应力,研发超声振动强化搅拌摩擦焊试验装置,开展6061-T6铝合金的焊接工艺试验。采用实时采集焊机电参数并将其转化成力矩和力的方法,测试超声振动作用下搅拌摩擦焊的焊接载荷,利用热电偶测试施加超声时的焊接热循环,通过体视显微镜和金相显微镜分别观测焊缝截面尺寸和接头微观组织,并与相同参数下常规搅拌摩擦焊的情况进行比对。研究结果表明,超声振动能够显著降低焊接轴向压力和搅拌头转矩,增大焊缝横截面尺寸,细化和均匀焊核区和热力影响区的晶粒组织。热循环的测量结果显示,超声振动的施加略微降低了测量点的焊接热循环峰值温度。分析认为,超声振动与搅拌头附近的塑性变形材料相互作用,降低了金属材料的屈服应力和流变应力,进而改变了原有的温度场,从而产生了优异的工艺效果。     

胶凝砂砾石过水围堰施工难点与对策分析

胶凝砂砾石围堰料源便利,优势突出,根据某工程围堰的施工过程遇到了地质条件变化、供料强度不足、质量控制标准修订、储料规划改变等难点,采取了针对性的对策,介绍CSG围堰施工管理的经验,对以后胶凝颗粒料筑坝施工具有重要参考、借鉴意义。     

关于岩土工程安全监测工程现场埋设施工技术的几个问题分析

为了保证监测数据的连续性、完整性、可靠性、及时性和准确性等,对监测施工提出了较高的要求。监测施工主要包括施工前准备、仪器现场检验率定、监测仪器安装、电缆连接及保护以及监测数据的采集及分析。