Dissimilar welding of aluminum alloys 2024 T3 and 7075 T6 by TIG process with double tungsten electrodes

The aim of this work is to study the metallurgical and mechanical properties of dissimilar assemblies of 2024 T3 and 7075 T6 structural hardening aluminum alloy by TIG twine electrode arc welding process. It will include a weld performed according to optimized welding parameters followed by a study of the macroscopic and microscopic evolution of the dissimilar assembly (2024–7075) using optical and scanning electron microscopy (SEM); In addition, the phase compositions were analyzed with an energy dispersive spectrometer (EDS). Tensile and microhardness tests were performed. The tensile fracture was observed by SEM. We have found that this process thins the weld bead and reduces the size of the heat affected zone (HAZ) of the welded joint. The microhardness is lower in the melted area and higher on the side of the area affected by the heat especially for 7075 alloy, resulting in brittle strength and a sudden drop in breaking strength.

Microstructural and Mechanical Properties of Welding and Thermal Spraying Coatings on Ductile Cast Iron

The subject of this work is to evaluate the influence and adhesion degree of different coating layers deposited on a ductile cast iron substrate by two different methods, thermal spraying and welding with and without use of an interlayer. Microstructures of different zones and interfaces of coated specimens are investigated using optical microscope and scanning electron microscope SEM. Also, the mechanical behavior was evaluated by tensile test. It is found that when stainless steel thermal spraying coating onto the ductile cast iron substrate, the use of the nickel-based interlayer Ni allowed us to mitigate the disadvantages of cracking at the interface. This is due to the mechanical effect of nickel plasticity. In the case of coating by welding, the use of nickel-based buttering ENi-CI allowed us to reduce the diffusion of graphite to stainless steel, resulting in a reduction in the formation of harder alloy carbides. Finally, the mechanicals tests in particular the tensile test shows that the coating by welding is effective but causes a structural hardening; on the other hand the coating realized by thermal spraying does not really present sufficient adhesion.

On the Energy Absorption of Combined Foam-Honeycomb Layered Structures

Analytical and numerical analyses are carried in order to reveal the importance of the topology of the cellular materials for their dynamic compaction. The aim is to distinguish between the deformation mechanisms and energy absorption of materials, which exhibit structural softening, such as out-of-plane loaded honeycomb, and structural hardening (foam). It is shown that the dynamic compaction of honeycombs does not obey the law of shock wave propagation and a new phenomenological model of the velocity attenuation in out-of plane loaded honeycomb is proposed. Comparisons with some currently available theoretical models of the dynamic compaction of cellular materials are discussed when paying attention to the effect of the material homogenization of the honeycomb on their response to impact loading. A numerical analysis of a bi-layer cellular structure comprising layers with dissimilar constitutive properties is carried out to reveal the possibility for the peak load reduction in cellular structures when subjected to impact loading. In the reported examples, a foam material (Alporas with density of 245 kg/m3) and hexagonal honeycomb made of aluminium alloy AA5056 and having densities of 60.46 kg/m3 and 96 kg/m3 are used.

Kinetic Study of Structural Hardening Mechanisms of PbCdBiSn and PbCdBiMg Alloys for the New Generation of Battery Grids

The study of the return to equilibrium state of PbCdBiSn and PbCdBiMg alloys has been studied. Indeed, two structural states were considered: raw casting alloy and rehomogenized alloy. The experimental temperatures are 20°C and 80°C. The latter temperature was selected because it corresponds to the temperature of ripening of battery grids and extreme temperature for operating a battery. We studied the kinetics of Pb2%Cd1%Bi0,5%Sn and Pb2%Cd1%Bi2%Mg. The activation energy of the alloy without tin remains less than the one with tin and approximate to that with Magnesium.

Structural Hardening of Excavator Teeth Used in Exploitation of Magmatic Rocks

The teeth of specialized excavators used in exploitation of magmatic rocks are made by forging from alloyed steels having 3.4%Mn, and the value of hardness less than 38HRC. The usual working time is about 15,000 hours.This paper estimates the possibility to make a structural hardening of the excavator teeth using the deposition by welding of hard layers. These hard layers are obtained by using the electrodes type Cr-W-V-Ti, having the hardness between 48 and 50HRC. In these conditions, the austenitic hard structures with complex carbides of W, V, Ti are developed.The presence of the hard layers on the active surfaces of teeth, deposited using an homologated technology, will allow to increase the life time of these components with minimum 30% in usually working conditions.

Study on Al-Si Alloys Properties Enhancement

The paper presents a study about aluminum alloy, allied with Si, Cu, Mn, Mg. The Al-Si-Cu-Mg alloys for foundry are used for parts strongly required and which work at high temperatures, due to their good wear resistance. The industrial Al-Cu alloys contain 12 % cooper, are hipo-eutectic and may be for foundry or deformable. By alloying with magnesium, the Al-Cu alloys become with remarkable properties of resistance and plastic deformation processing. The improvement of mechanical characteristics for Al-Si alloys is realized with metals which forms the intermediate phases with silicon or aluminum, with variable solubility in solid state and which permits the structural hardening by heat treatments (quenching and ageing). From the analysis of dilatogramms, grouped for each sample, with the specific initial length, subjected to successive heating, from ambiance temperature up to 500°C, it is found that, with the appearance of ageing phenomena, on the samples aren’t significant modifications for elongation (few microns), only different may be the form of elongation-temperature curve. This analysis permits the determination of experimental data, regarding the behavior of Al-Si alloy subjected to heat treatments and repeated warming. Therefore, the Al-Si-Cu-Mg alloys, for foundry, are used for manufacture the parts strong required and which work at high temperatures, like pistons for engines with internal burn, parts for machines and reinforcements construction, due to their high usage resistance.