Formation of Heterogeneous Microstructure in AA1050/AA5052/AA6061/AA1050 Layered Sheet Processed by Cold Roll-Bonding and Subsequent Annealing

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA5052/AA1050 four-layer clad sheet and subsequently annealed. Three types of aluminum alloy sheets such as AA1050, AA6061 and AA5052 with 2 mm thickness, 40 mm width and 300 mm length were stacked up each other after such surface treatment as degreasing and wire brushing, then reduced to a thickness of 2 mm by multi-pass cold rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA1050/AA6061/AA5052/AA1050 clad sheet was then annealed for 0.5 h at 200~400 °C. Microstructures of the as-roll bonded and subsequently annealed aluminum sheets are investigated by electron back scatter diffraction (EBSD) measurement. After rolling, the roll-bonded AA1050/AA5052/AA6061/AA1050 sheet showed a typical deformation structure that the grains are largely elongated to the rolling direction. However, after annealing, it exhibits a very heterogeneous structure consisting of both deformation structure and recrystallization structure containing nanometer order grains. The formation of this heterogeneous structure and texture with annealing is investigated in detail through EBSD analysis.

Surface Modification of Rusted Rebar and Enhanced Passivation/Anticorrosion Performance in Simulated Concrete Pore Solutions with Different Alkalinity

Naturally exposed rusted rebar has been widely used for the production of reinforced concrete. However, rusted rebar is prone to corrosion under chloride ion (Cl−) contamination and/or at a low alkalinity of concrete. This study employed two surface modification methods, sand blasting and wire brushing, to augment the corrosion resistance of naturally exposed rusted rebar. Electrochemical tests revealed that the surface-modified rebar displayed a significant improvement of passivation in the concrete alkaline environment and anticorrosion performance in both the Cl− free and Cl−-containing simulated concrete pore solutions of different alkalinity. The enhanced performance was mainly due to the elimination of the rust layer and the direct exposure of the fresh metallic surface to the alkaline medium. Moreover, the effect of surface nanograins on the intensified passive film led to the best passivation performance of the wire-brushed rebar. The overall findings demonstrate that the two developed methods were conducive to the passivation and anticorrosion performance of the rusted rebar and thereby hold great promise for improving the service life of the reinforced concrete structures.

Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials

The structural capacity of 3D printed components mainly depends on the inter-layer bonding strength between the different layers. This bond strength is affected by many parameters (e.g. moisture content of the substrate, time gap, surface roughness,..) and any mismatch in properties of the cementitious material may lead to early failure. A common technique to improve inter-layer bonding strength between a substrate and a newly added layer is modifying the substrate surface. For the purpose of this research, a custom-made 3D printing apparatus is used to simulate the printing process and layered specimens with a different delay time (0 and 30 minutes) are manufactured with different surface modification techniques (wire brushing, addition of sand or cement and moisturizing substrate layer). The surface roughness was measured and the effect of the modification technique on the inter-layer-bonding strength was investigated. Results showed that the most effective way to increase the inter-layer bonding is increasing the surface roughness by a comb. This creates a kind of interlock system that will provide a higher inter-layer strength. The compressive strength is most influenced by the addition of cement, where the changing W/C-ratio will create a higher degree of hydration and consequently a higher strength.

X-Ray Diffraction Technique for Residual Stress Measurement in NiCrMo Alloy Weld Metal

In the present work, residual stresses in nickel-based (Ni 625) superalloy weld metal of a 9%Ni steel-welded joint were measured by X-ray diffraction (XRD). This technique presents some difficulties in performing measurements in coarse and preferentially oriented weld metal microstructures. It is proposed a preliminary surface treatment by rotating steel wire brushing to perform the stress analysis through XRD technique possible for this kind of material. Stress measurements with proposed XRD technique showed that the stress state in Ni 625 weld metal on the outside surface of the welded joint is characterised by tensile stresses in the transverse and longitudinal directions, while compressive transverse and tensile longitudinal residual stresses are developed in the root pass region.

Effect of Surface Nanocrystallization on Corrosion Resistance of the Conformed Cu-0.4%Mg Alloy in NaCl Solution

Surface nano-crystallization (SNC) of a conform-extruded Cu-0.4 wt.% Mg alloy was successfully conducted by high-speed rotating wire-brushing to obtain the deformed zone with dislocation cells and nanocrystallines. SNC promotes the anodic dissolution and corrosion rate of the Cu-Mg alloy in the initial stage of immersion corrosion in 0.1 M NaCl solution. The weakened corrosion resistance is mainly attributed to the higher corrosion activity of SNC-treated alloy. With extending the immersion time, the SNC-treated alloy slows the corrosion rate dramatically and exhibits uniform dissolution of the surface. The formation of the dense corrosion products leads to the improvement of overall corrosion performance. It indicates that the SNC-treated Cu-Mg alloy can function reliably for a longer duration in a corrosive environment.

Analysis of deburring effectiveness and surface layer properties around edges of workpieces made of 7075 aluminium alloy

Purpose This paper aims to present a comprehensive analysis of deburring effectiveness and surface layer properties after deburring process by wire brushing from milled 7075 aluminium alloys objects. Edge states (rounding, chamfering), surface roughness around the edge, microhardness and residual stress distribution were analyzed. Design/methodology/approach During the machining process, undesirable phenomenon occurs, which is the formation of burrs at the edges of workpieces. They occur in most elements formed by machining. There are many methods that can be used for deburring, but in the case of large components, typical of aerospace industry, using certain methods becomes difficult or uneconomic. Taking advantage of the fact that a part is mounted on the machine, it is advisable to make deburring operation the last action. This operation can be carried out by wire brushing. Findings On the basis of conducted studies, it was demonstrated that it was possible to choose such technological brushing conditions as to ensure an effective process of deburring, form appropriate edge state and generate the desired surface layer properties. Practical implications The method presented in the article allows for efficient, automatic deburring, especially for large components made of 7075 aluminium alloy. This eliminates manual, time-consuming methods of removing burrs by locksmiths. Moreover, the results allow to evaluate changes occurring in the surface layer after brushing process. Originality/value Results of brushing experiment provide full information on selection of technological parameters to obtain the required surface roughness and edge state. Moreover, analysis of surface layer properties (microhardness, residual stress) allows to assess the degree of impact hitting fibre on the workpiece.

Dynamic Diameter Determination of Circular Brushes

After milling process burrs can form as a result of plastic deformation of the material. Wire brushing can be used as a fully automated method of deburring on machining centres. In order to provide the same effects after brush change it is important to precisely determine the tool diameter. The article presents the method of dynamic diameter determination of circular brushes, which is the diameter of the brush during rotation.

Surface Microstructure Modification by Wire-Brushing and Annealing and its Effect on Tensile Ductility and Bendability of Mg Sheet

A wire brushing and annealing process is developed and utilized to modify the surface layer microstructure of AZ31 magnesium sheet material and assess its effect on uniaxial tensile ductility and bendability. Wire brushing process utilizing fine brass wires is optimized to minimize deterioration in original surface quality by varying spindle rotational speed and depth of cut per wire brushing pass. Wire brushed material is then subjected to annealing to recrystallize the severely deformed surface layer. Rotational speed of 2800 RPM, feed rate of 1 mm/s, and a very small depth of cut coupled with annealing at 200 °C for 60 minutes results in a refined grain layer of grain size 5.5 μm and depth 30 μm on the surface. A texture study of wire brushed and annealed surface by X-ray diffraction reveals a randomized texture on the surface. Refined grain size and randomized texture result in about 38% enhancement in uniaxial tensile elongation in AZ31 compared to non-wire brushed annealed material. The role of surface microstructure and texture in improving sheet tensile ductility and bendability is discussed.

INTERFACE SHEAR STRENGTH OF CONCRETE-TO-CONCRETE BOND WITH AND WITHOUT PROJECTING STEEL REINFORCEMENT

Composite concrete consists of two elements cast at different times which are the concrete base and concrete topping. To achieve composite action, interface shear strength must be sufficient to resist the sliding motion between the two concrete surfaces in contact. The interface shear strength is mainly depended on concrete cohesion, friction and dowel action. A total of 36 “push-off” tests were performed to study the interface shear strength and to assess the influence of surface texture and steel reinforcement crossing the interface. Three different concrete base surfaces are prepared which include smooth or “left as-cast”, roughened by wire-brushing in the transverse direction and steel reinforcement projecting from the concrete base. Eurocode 2 provides design equations for determining the interface shear strength with different surface textures and also the one where projecting steel reinforcement crosses the interface. The experimental results show that the transverse roughened surface produced the highest interface shear strength of 1.89 N/mm2 (σn = 0 N/mm2), 4.69 N/mm2 (σn = 0.5 N/mm2), 5.97 N/mm2 (σn = 1.0 N/mm2) and 6.42 N/mm2 (σn = 1.5 N/mm2) compared with the other surface textures. This proves that the increase in the degree of roughness contributes to higher concrete cohesion and friction coefficient. However, for the surface with projecting steel reinforcement, the failure is not sudden as experienced by the surface without one. This is due to the contribution of the clamping stress from the dowel action of the steel reinforcements. Meanwhile, for specimens without any projecting steel reinforcements, the interface shear strength depended solely on friction and concrete cohesion of the surface textures. The interface shear strength of surface with and without the projecting steel reinforcement can be predicted using the Mohr-Coulomb failure envelope. This paper also proposed design expressions for concrete-to-concrete bond on surfaces provided with and without projecting steel reinforcement that can be adopted in Eurocode 2.