Papers by Keyword: Bi-Metal

Abstract: The paper presents technologies for the manufacturing of modulated bi-metal elements, used as interchangeable reinforcement, according to patent RO129865. The bi-metal was developed by surface build-up of functional layers that have increased hardness, on a low alloyed steel substrate, so as to ensure maximum lifespan in exploitation. Welded layers deposited on active areas has a thickness of 3 mm and have high hardness (about 50-60 HRC) in order to ensure a good resistance to wear by abrasion, possibly combined with fatigue, erosion or corrosion. The modulated elements sizes are equal to or higher than the wear additions, up to 10%, being dimensioned on the principles of preventive-repetitive maintenance. The interchangeable bi-metal elements are welded on the steel components of machines, used for hot or cold processing of parts and semi-finished products manufactured in series.

Abstract: Thixo-forging has been proved to be able to fabricate bi-metal parts with a complex outline and a relatively regular interface economically. These products have potential applications on high volume stability radiators, brakes, and pistons. However, it is very difficult to evaluate the curved interfaces by micro observations. In this work, Al-22%Si-Cu/Al-7%Si-Mg bi-metal parts were fabricated by thixo-forging; state of the interfaces of the bi-metal parts was investigated by X-ray flaw detector observations and tensile test; optical microscope (OM) observation and scan electron microscope (SEM) observation were applied to assist the analysis. The results show that the metallurgical bonding of the interfaces is of good quality. No large scale flaw was found on the interface in X-ray flaw detector observation. It was found that higher forging pressure decreased the size of the crack on the interface and in the matrix. However, higher forging pressure can slightly improve tensile strength. Large ratio of fresh interface relates to original interface resulted in a slightly better tensile strength. Without heat-treatment, the bi-metal forgings have an average tensile strength of 106 MPa. T6 heat treatment blunted the blades of the plate like crack and nodulized the defects, T6 heat treatment also decreased the size of the Si particles. As a result, the average tensile strength of the bi-metal forgings increased to 200 MPa.

Abstract: This paper presents an experiment conducted in Explosia, a.s., Pardubice. A bimetal prepared of AZ 31 Mg alloy - CrNi austenitic steel was tested in various conditions, and consequently its quality was assessed. Focus was particularly on the impact of atmosphere and vacuum on the interface character of the metals (bimetals) prepared by explosion. Parallel placement of the materials being welded was used for welding in both vacuum and air atmosphere. Welding sets were designed and manufactured. The welding parameters and conditions were set up utilising the available computational means, and then verified by simulation in ANSYS engineering-scientific program. Used was Semtex S 35, a loose explosive, as well as Startline 12, an initiation explosive. Bimetal was fabricated in the air atmosphere at the detonation speed 2613 m.s^-1 and in vacuum at the detonation speed 2597 m.s^-1. Quality of bimetals was assessed by optical microscopy, measuring deformations by a 3D scanner, measuring microhardness and also by EDX microanalysis.

Abstract: Peculiarities of formation of solid-state joining of the parts for bimetallic heat exchanger are considered. For solid-state activation of the surfaces, being joined, the layer-activator (liquid gallium) is used. Inter-granular segregation of an activator along the grain of the alloy-matrix is rapid and deep, which leads to polygonal structure in the diffusion zone. A negative fact for such joints is the brittleness of materials after intermetallic phase transformation of the chemical elements of alloy-matrix with gallium. The joint formed with an increasing of volume of the diffusion zone after rotation of newly formed phases at growth. Rotation of grains leads to emergence of high local internal stresses. Excess of an activator may be a reason for generation and distribution of main cracks. Indentation allows recording an abnormal decrease of the micro-hardness in grain boundary area. Obtained data of the Young's modulus, micro-hardness and coefficient of plasticity, with spectral mapping of chemical elements and phase analysis are allowed to exactly specify structural components that are the initiators of the materials stress state and are the reason for local cracks.

Abstract: According to the hammer crusher working condition, a kind of dual liquid bimetal composite casting hammer was developed. Its service life is three times than that of high manganese steel. It improves the wear resistance and increases production efficiency significantly, and is welcomed by user deeply.

Abstract: Bimetal of high-tin aluminum alloy and steel was fabricated by cold-rolling process; microstructure, bonding strength and bonding mechanism for bonding interface of the bimetal were investigated under cold-rolling and recrystallization annealing state, respectively. Experimental results indicate that tin phase of bimetal in cold-rolling state shows a belt type distribution, however, it, in recrystallization annealing state, is uniformly distributed just like some “isolated islands”. A well bonding interface, between layers of high–tin aluminum alloy and pure aluminum, can be obtained, and it is difficult to distinguish one layer from the other; but the interface, between layers of low-carbon steel back and pure aluminum, is clear and uneven. And meanwhile, bonding mechanism of bimetal interface, in cold-rolling state, is cold pressure welding and mechanical occluding, But it, in recrystallization annealing state, is cold pressure welding, mechanical occluding, and metallurgic bonding. After recrystallization annealing, at 350°C for 2h,the bonding strength of bimetal approaches to 92.4MPa, which is about 26% higher than that of cold-rolling state.

Abstract: A cast iron/low carbon steel sandwich-structured bimetal fabricated through composite casting, followed by hot rolling and hot compression (40% reduction) in a vacuum, and water quenched using Gleeble 3500 thermomechanical simulator. The microstructure of a predominantly martensitic structure is transferred to a matrix with an amount of austenite. The measured results show that the macro-hardness is significantly lower due to the evolution of matrix. A considerable amount of secondary carbides were precipitated from the matrix. This study also shows that a significant difference in the value of coefficient of friction (COF) at the end when hot rolling (HR) was tested under three sets of sliding wear conditions, while those for hot rolling and heat treatment (HT) tends to be merged. An increased wear resistance of interfacial zone is expectable.

Abstract: For the characteristics of the hammer handle is under bending stress and impact constantly alternating and the the main of the hammer is Withstand strong impact and friction in use，the paper designed a new type of composite casting process of hammerhead. It has two wear block imbedding in the below of the hammer ，and it set in on both sides of the axis of the hummer wiche with Inverted trapezoidal dovetail structure. The wear block was cast by high chromium cast iron, and it is properly heat treatment and surface cleaning before casting, but Into the mold after re-heated to temperature above 600 °C，At the same time，poured into the cast high-manganese steel quickly，so the block and hammer handle fused together，the block of composite hammer does not wear off in the use, and the wear resistance of the hummer improved significantly.

Abstract: A challenge method composed of digital image correlation (DIC) method, circle coordinate grid technology and finite element (FE) software to conduct strain measurement of bimetal is presented. This approach can carry out the prediction and measurement of strain. The coordinate grids are painted on top and bottom surface of bimetal when experiment and simulate specimen. Each node is named a fixed number in turn, and these numbers can precisely help to identify the same name point between FE software and the experiments specimen. The bimetal sheet has been tested using DIC software, circle center of the coordinates points can be accurately identify on the surface of bimetal. The changing of distance between adjacent points is computed to construct the forming limit diagram before and after forming. It is an effective means to evaluate the forming performance of bimetal and verify the reasonable of FE analysis results. 2A12 metal is conducted experiment using the challenge method in this paper, bimetal has not conduct experiment due to some reasons.

Abstract: This paper provides an analysis of a co-extrusion process. The compound consists of the sleeve material, aluminum, and the core material, magnesium. It is imperative to produce impeccable compounds without cracks in the interface. Therefore, a simple indicating value for damaging effects during the process is necessary. In the numerical simulation the compound quality is noticeable by the current macro mechanical criterion of axial strain difference. A statistical analysis verifies this criterion as an adequate quality criterion. By means of this criterion it is possible to define a stable process window for the co-extrusion process.