Zoltán Weltsch

Alloying Effects on Wetting Ability of Diluted Ag-Based Melts on Ceramic Substrates

The wetting angles (Θ) of Ag-M based melts (M: Cd, Sn, Sb) on graphite and Al2O3 substrates are compared. Despite of the inert chemical character and the similar surface roughness of substrate materials, the wetting angle is smaller on the Al2O3. The compositional and concentration dependence of Θ exhibits similar trends, than that, observed in the bulk transport properties such as the specific electrical resistance or the thermopower obtained on the same alloys in solid state. No segregation effects can be detected on the solidified metal drops.

Compositional and Stress-Sensitive Factors during the Thermopower Characterization of Single Phase Crystalline and Glassy Alloys

For the study of stress state in engineering alloys, the thermopower (S) measurement could be acceptable method after a suitable calibration (fitting the S value to the change of well known other physical parameters like the magnetic coercive force, hardness or strength increase during various thermomechanical treatments). For this purpose a simple equipment is constructed and built by which the S shift can be measured versus the increasing mechanical tensile load. The first results will be published in this paper, obtained on various metallic glass ribbons.

Wetting Ability of Ag Based Molten Alloys on Graphite Substrate

The wetting angle (Θ) of molten Ag (Zn, Cu, Ga) drops on graphite substrate is investigated. A texture formation was found in the substrate/drop interphase region after solidification. The enrichment (segregation) of Ag atoms in the interface layer was observed in the Ag-Cu alloy, and unexpected mixing between graphite substrate and the Ag-Ga melt was also detected in the solidified structure.

Wetting properties of Nd:YAG laser treated copper by SAC solders

Purpose This paper aims to discuss the effect of surface treatment on the wettability between copper and a lead-free solder paste. The industrial applications of laser technologies are increasing constantly. A specific laser treatment can modify the surface energy of copper and affect the wetting properties. Design/methodology/approach The surfaces of copper plates were treated using an Nd:YAG laser with varying laser powers. After laser surface treatment, wetting experiments were performed between the copper plates and SAC305 lead-free solder paste. The effect of laser treatment on copper surface was analysed using optical microscopy and scanning electron microscopy (SEM). Findings The experimental results showed that the wetting contact angles changed with the variation in laser power. Furthermore, it means that the surface energy of copper plates was changed by the laser treatment. The results demonstrated that the contact angles also changed when a different soldering paste was used. Originality/value Previous laser surface treatment can be a possible way to optimize the wettability between solders and substrates and to increase the quality of the soldered joints.

The Relation between the Surface Tension and the Bulk Properties of Diluted Silver Based Melts

The wettability of graphite by the Ag-M based (M: Cd, In Sn, Sb) liquid alloys was measured using the sessile drop method at a temperature interval of 1273 1473 K. Except the Ag-Cd alloys, the investigated systems exhibit worse wettability than that of Ag (host metal) melt, within the investigated temperature range. The compositional and concentration dependence of contact angle (Θ) exhibits similar trends, than the residual resistivity change measured in the same alloys in solid state. Nevertheless, the measured segregation effects during the solidification are not significant.

Prediction of stress- and strain-based forming limits of automotive thin sheets by numerical, theoretical and experimental methods

Forming limit is a complex concept of limit values related to the onset of local necking in the sheet metal. In cold sheet metal forming, major and minor limit strains are influenced by the sheet thickness, strain path (deformation history) as well as material parameters and microstructure. Forming Limit Curves are plotted in e1 – e2 coordinate system providing the classic strain-based Forming Limit Diagram (FLD). Using the appropriate constitutive model, the limit strains can be changed into the stress-based Forming Limit Diagram (SFLD), irrespective of the strain path. This study is about the effect of the hardening model parameters on defining of limit stress values during Nakazima tests for automotive dual phase (DP) steels. Five limit strain pairs were specified experimentally with the loading of five different sheet geometries, which performed different strain-paths from pure shear (−2e2=e1) up to biaxial stretching (e2=e1). The former works of Hill, Levy-Tyne and Keeler-Brazier made possible some kind of theoretical strain determination, too. This was followed by the stress calculation based on the experimental and theoretical strain data. Since the n exponent in the Nadai expression is varying with the strain at some DP steels, we applied the least-squares method to fit other hardening model parameters (Ludwik, Voce, Hockett-Sherby) to calculate the stress fields belonging to each limit strains. The results showed that each model parameters could produce some discrepancies between the limit stress states in the range of higher equivalent strains than uniaxial stretching. The calculated hardening models were imported to FE code to extend and validate the results by numerical simulations.

Complex Process Monitoring of Cutting Hybrid Metal Structures

The behavior of the cutting edge of the tool during the cutting process, especially the impact of the boundary surfaces of different materials has been studied by several authors. In this paper the latest results, achieved by our team, are reported. Several methods of the complex diagnostics of the cutting process of metal composite structures, including cutting force measurement, vibration analysis, high speed camera and thermography were successfully used for this purpose. It was found, that the boundary surface of the different materials has a big impact on the cutting force, the vibration and the temperature of the tool, which can be monitored very effectively with this complex technique.