Zbigniew Mirski

Wettability of hardmetal surfaces prepared for brazing with various methods

Hardmetals belong to the materials hardly wettable by liquid brazing alloys, so they should not be brazed without removing the surface layer after sintering. In the paper, mechanical and chemical methods of preparing a hardmetal surface for brazing are discussed. Special attention is paid to the electrolytic etching method that gives very good energetic properties to surfaces of hardly wettable materials. Electrolytic etching of hardmetals consists in anodic dissolution of tungsten carbide grains in water solution of alkaline metal hydroxides. The α phase (WC) is removed from surfaces of carbide preforms, leaving the much better wettable β phase (Co-W-C). Cobalt does not show amphoteric properties, so it does not dissolve in bases. With regard to brazing, besides significant development of the surface, an especially profitable feature of this method is isolating the metallic cobalt phase, which allows easier wetting by brazing alloys. On the grounds of surface roughness measurements, parameters of electrolytic etching were determined to remove WC grains from surfaces of carbide performs and to obtain much higher Co fraction on the brazed surface. The presented results are based on measurements of wetting angles on B40 hardmetal surfaces, isolated α and β phases and C45 steel, as well as on EDX cobalt analysis on hardmetal surfaces.

Possibilities of laser-beam joining cemented carbides to steel

Welded joints of cemented carbides with steel are commonly present in tool production, mainly those used in the machining and mining industry. The article presents possibilities of joining cemented carbides H10S and G10 with steel C45 using laser radiation. These are the first innovative experiments carried out in Poland. Joints between cemented carbides and steel were made both directly and using spacers between the materials to be joined, which were made of copper, triple-layer solder Ag49/Cu and nickel. The joining trials were carried out at the Laser Technology Centre of the Institute of welding in Gliwice. A Triumpf disc laser (λ = 1030 nm) Tru-Disc 12002 with output power of 12 kW was used for this purpose. The laser beam was focused mostly on the steel surface to avoid direct interaction between the laser beam and the structure of cemented carbides. The assessment of joints of cemented carbides with steel C45 was conducted on the basis of metallographic evaluation, EDX analyses and microhardness measurements.

Soldering of aluminium with copper

Soldering of aluminium with copper becomes more significant, because of relatively low process temperature of about 400–450°C. It is applied not only in electrotechnical industry, in joining Al–Cu conductors, but also in cooling and air-conditioning equipment and in solar construction of collectors (Winiowski A. Lutowanie twarde aluminium i jegostopów – nowe trendy technologiczne, Biuletyn Instytutu Spawalnictwa, nr 6/2000, Fontargen GmbH. Löten in der Kälte- und Klimatechnik, Eisenberg. 2001 and Fontargen GmbH. Aluminium-Löten. Eisenberg 2003). In this paper, problems concerning Al–Cu soldering are presented. For soldering, zinc solders with the addition of 2, 4, and 15 wt% Al have been used. Results of wettability and spread factor measurements of zinc solders on aluminium and copper surface, as well as metallography, microhardness, and shearing tests of Al–Cu joints are presented. Effects of copper pipes with aluminium plate soldering with application of flux coating solders are also described.

The aggressive influence of lead-free solders and the protection of soldering devices against damage

The article presents the influence of lead-free solders on SnAg3.8Cu0.7 and SnCu0.7 tin matrices, as well as SnPb37 solder on the solubilization of copper under various conditions during dip soldering. The influence of lead-free solders, higher soldering temperatures and mobile soldering baths on the intensified effects of copper solubilization is demonstrated. Elements of soldering facilities coming into contact with SnCu3 solder-filled soldering bath are subject to solubilization and damage as a result. Protection of these elements and increase of their resistance by covering them with a ceramic layer based on Al2O3–TiO2 oxides was suggested.

Powder solders for hard soldering of aluminium and its alloys

Nowadays, aluminium and its alloys are successfully joined using various welding methods in many fields of technology. These include hard soldering, thanks to which bonding may be obtained which meets especially high requirements. Application of aluminium and its alloys in soldered joints is common in the construction of heat exchangers, e.g. heating, cooling and air-conditioning systems, as well as in electric machines and connections for conducting electric current. In the last 20 years, hard soldering has become especially important in the construction of aluminium air-conditioning systems for the automotive industry and air conditioners for building units. Aluminium flame soldering should be performed with carefully selected soldering technology. Depending on whether this is manual or mechanized soldering, the choice of filler should be considered, i.e. fluxes, controlled atmospheres or solders. Thanks to their great running quality, silumin-based solders containing 5–12% by weight silicon are most frequently used for hard soldering of aluminium and its alloys. Among these, ordinary solders A1Si12, AlSi10 and AlSi7,5 are most often used in practice. This paper presents examples of flame soldering using powder solders. These were manufactured from a Nocolok brand made of AlSi12 alloy and non-corrosive flux with a thickness of 0.3mm. Due to flux activity temperatures ranging from 565 to 5728C, close to the solder melting temperature, it is not recommended to use these materials separately for manual soldering. However, great results are obtainable using these materials under oven soldering conditions, in a controlled atmosphere, where the soldering temperature may be precisely specified. Joining of AlSi12 solder with Nocolok flux in the form of a powder wire facilitates manual flame soldering, even under difficult assembly conditions.