In this study, the mechanical properties and microstructure of a surface hardenings coating layers formed by laser cladding using bulk metallic glass (BMG)

Recently, in the automobile industry, it has become necessary to increase the fuel efficiency and the safety regulations to make the vehicle lightweight. Therefore, it is necessary to manufacture the dual phase steel, the complex phase steel, the MS steel, the TRIP steel, and TWIP have been increasingly applied to high strength steel with a tensile strength of 700MPa or more. In order to apply ultra high tensile steel to the body, welding process is essential. Resistance spot welding, which is advantageous in terms of cost, is applied more than 80% in body welding. It is generally known that ultra high tensile strength steel has poor weldability because it increases the alloy element content to improve strength. In the case of resistance spot welding of ultra high tensile steel, it has been reported that the proper welding condition area is reduced and interfacial fracture and partial interfacial fracture occur in the weld zone. In order to overcome such problems, researches on welding quality judgment that can predict the defect and quality in real time are actively conducted. In this study, the dynamic resistance of the weld is monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for welding quality determination are extracted from the dynamic resistance pattern. Using the analyzed factors, a regression model that could estimate weld strength was developed. Two regression equations of model were suggested depending on the factors, and it was showed that the model developed by backward elimination method was effective one for weld quality estimation. Based on this, a regression model that can be applied to the field was suggested.

Abstract. This study evaluated the mechanical properties and the microstructure of a surface hardness coating layer formed by laser cladding using a Bulk Metallic Glass (BMG) wire. The mechanical properties were measured by tensile strength test and micro-hardness test; microstructure and grain structure were analyzed by using a high-resolution scanning electron microscope and a transmission electron microscope. Surface coating was carried out by laser cladding and the GTAW process. The tensile strengths of the laser-cladded and GTAW coating layers were 2.0GPa and 1.7GPa, respectively. The tensile strength and micro hardness of the laser-cladded coating layer were about 15% and 14.3% higher than those of the GTAW coating layer, respectively. The laser-cladded coating layer showed finer grains and fewer dendrites due to their reduced distribution. The microstructure of the BMG coated layer showed a mix of α-Fe phase and amorphous phase.Keywords: Welding, GTAW, Laser cladding, BMG, Surface hardness coating, G.1-AW Mechanical PropertiesAs shown in Fig.1(a), the yield strengths of STS316L, GTAW, and Laser Cladding coated specimens were 292.1, 360.7, and 378.9 MPa, and the tensile strengths were 591.8, 534.8, and 568.9 MPa, respectively. The tensile strength of the substrate (STS316L) was higher than those of GTAW and Laser Cladding coated specimens by 9.63% and 3.86%, respectively, but the yield strengths of GTAW and laser cladding coated specimens were higher than that of the substrate (STS316L) by 19.02% and 22.91%, respectively.Generally, yield strength is a more important mechanical property than tensile strength for metals used in structural products. This is because elastic deformation does not affect a product's appearance, but plastic deformation changes a product's size or appearance, decreasing a product's value. The yield strength of the coating layer can be obtained by using Eq. (1) as follows.

This study proposes an structure that fixes the shielding device to two parts of the board by its two arranged clips. Said structure evenly distributes its loading/unloading load of the board and maintains the flatness of soldering area of the board. The structure of this study comprises a base part fixed to a printed circuit board and a clip part fixing a side wall of a shield can to the board, wherein the clip part is constituted with two clips fixable to two part of the shield can. Also, the structure of this study comprises a dented groove in order to easily solder the base part of clips and the printed circuit board. A mechanism is established and a design parameter was determined by a structure analysis and a vibration mode analysis. A single purpose machine for the production of the product was developed, the final workpiece was produced and the measuring-data and the computered-data was compared and reviewed.

The grating is the main purpose of drainage in civil engineering, architecture. This study examined the change and stress distribution by simulating three models of Vertical type grating structures that reduced the resistibility in respect of velocity rather than horizontal type grating and to design a grating with the optimal grating gap. The vertical type and horizontal type grating were compared in terms of the maximum stress and strain to identify the better product. Keywords :