Mikrostruktura i karakterizacija elektromagnetno lijevanih Al 2024 legiranih ingota

This paper presents the investigation into the possibility for application of production process for casting aluminum alloys under the influence of electromagnetic field. The presented results were obtained from microstructure examination of Al alloy 2024 ingots casted with or without electromagnetic field. The microstructure characterization shows that under the influence of low-frequency (30-50 Hz) electromagnetic field it is possible to obtain finer and more homogeneous microstructure with reduced porosity. In the end, it is obvious in which way the operation parameters should be varied in order to get a good quality of ingots.U radu je prikazana mogućnost primjene tehnološkog postupka lijevanja aluminijskih legura pod djelovanjem elektromagnetnog polja. Prikazani rezultati su mikrostrukturna analiza uzoraka aluminijske legure Al 2024 koji su dobijeni kontinuiranim lijevanjem pod djelovanjem i bez djelovanja elektromagnetnog polja. Rezultati pokazuju da se pod djelovanjem elektromagnetnog polja niskih frekvencija (30-50 Hz) dobija finija, po presjeku homogenija mikrostruktura sa reduciranom pojavom poroznosti. Na kraju, na temelju dobijenih rezultata može se zaključiti koji bi radni parametri bili optimalni kako bi se dobili odlijevci zadovoljavajuće kakvoće

Mikrostruktura i karakterizacija elektromagnetno lijevanih Al 2024 legiranih ingota

This paper presents the investigation into the possibility for application of production process for casting aluminum alloys under the influence of electromagnetic field. The presented results were obtained from microstructure examination of Al alloy 2024 ingots casted with or without electromagnetic field. The microstructure characterization shows that under the influence of low-frequency (30-50 Hz) electromagnetic field it is possible to obtain finer and more homogeneous microstructure with reduced porosity. In the end, it is obvious in which way the operation parameters should be varied in order to get a good quality of ingots.U radu je prikazana mogućnost primjene tehnološkog postupka lijevanja aluminijskih legura pod djelovanjem elektromagnetnog polja. Prikazani rezultati su mikrostrukturna analiza uzoraka aluminijske legure Al 2024 koji su dobijeni kontinuiranim lijevanjem pod djelovanjem i bez djelovanja elektromagnetnog polja. Rezultati pokazuju da se pod djelovanjem elektromagnetnog polja niskih frekvencija (30-50 Hz) dobija finija, po presjeku homogenija mikrostruktura sa reduciranom pojavom poroznosti. Na kraju, na temelju dobijenih rezultata može se zaključiti koji bi radni parametri bili optimalni kako bi se dobili odlijevci zadovoljavajuće kakvoće

Processes at the inetrface molten metal-sand mold

The processes that take place at the liquid metal-sand mold interface during the casting and crystallization of metal were studied in this paper. The mold was made using the CO2 – method, with the addition of active components, such as: MgO, TiO2, AlK(SO4)2 and Na2SO4. At the liquid steel pouring temperature, these active components undergo decomposition in the mold, caused by heat release during pouring, crystallization and cooling of castings. Silicates, which have an important influence on casting surface quality, are formed as a result of the interaction between the mould material and liquid steel

Mogućnost povećanja efikasnosti proizvodnje Al legura primjenom elektromagnetnog polja

The relationships between electromagnetic frequency, microstructure and mechanical properties of continuous casting aluminum alloys were studied in this paper. EN AW 2024 and EN AW 2007 aluminum alloys ingots were produced by electromagnetic continuous casting process. The microstructure and mechanical properties of as cast ingots were examined. The results showed that electromagnetic field, especially low frequency electromagnetic field, greatly influenced the microstructure and mechanical properties of as cast ingots. The significant energy savings and product quality can be achieved by the application of a proper frequency.U radu je prikazan utjecaj frekvencije na mikrostrukturu i mehanička svojstva Al legura dobijenih kontinuiranim elektromagnetnim postupkom ljevanja. Ispitivanja su obavljena sa dvije legure EN AW 2024 i EN AW 2007. Mikrostrukturna i mehanička karakterizacija urađena je na uzorcima u ljevanom stanju. Rezultati istraživanja pokazuju da elektromagnetno polje, posebno polje niže frekvencije, utječe na mikrostrukturu i mehanička svojstva ljevanih ingota. Na osnovu dobijenih rezultata može se zaključiti da se primjenom elektromagnetnog polja odgovarajuće frekvencije može postići značajna ušteda energije kao i poboljšanje kvaliteta dobijenih ingota

Improving the quality of Al-alloys hot forging

Aluminium forgings provide the following advantages: high strength and low weight, good corrosion resistance (for most aluminium alloys), the fibre (grain) structure can be arranged to correspond to the main loading direction leading to high strength and fatigue properties. High precision forgings are designed keeping the following aspects in mind: increasing the accuracy of the component, increasing the fatigue strength, reducing the mass of the component, reducing the amount of machining and increasing the economy. This paper systematically discusses the parameters influencing the accuracy of forgings and forging tool life. Detailed characteristics of alloys AlZnMgCu1.5 (EN-AW 7075) for forging are described. By using the software Simufact. Forming for real part and production conditions, appropriate numerical modelling and recommendations for improved manufacturing have been made.The authors wish to acknowledge the financial support from the Ministry of Education and Science of the Republic Serbia through the project TR 34002.Publishe

CHANGING OF TENSION STRESS OF IRONED ALUMINIUM WORK PIECE WALL

The size and distribution of contact stresses in strain zone influence the stress-strain state of y formed work piece, the possibility for successful forming as well as the force needed for forming execution. The effects of friction forces in strain zone are various; on the outer surface (between work piece and die) these forces (FfrD) increase tension stresses, and on the inner surface (between work piece and punch, forces FfrP) they relieve the critical section, reducing stresses in the wall of work piece which is ironed. That is the main reason for achievement of high strain ratios and realization of the significant increase of relative depth at drawing. The increase of friction on punch side reduces the critical tension stress, but the total drawing force increases. In the course of that, the force FfrP must not increase so much that, on contact surface of work piece, it leads to appearance of rough intrusions and micro-welding (or adhesion) of metal particles of work piece on tool, because it would lead to damaging of work piece and tool and make difficult the removal of work piece from the punch. In this paper, the analyses of the influence of different parameters (die gradient angle, lubricant on die and punch, punch roughness, tool material etc) on stress of tension of ironed work piece wall were made.Publishe

Influence of contact conditions and strain path on stretching of steel and Al-alloy sheet metals

Biaxial tension – stretching of sheet metals is one of characteristic stress-strainschemes, which in the course of sheet metal forming by deep drawing may exist in particular work piece zones or may dominate completely (Erichsen’s test). In such forming conditions, tribological conditions of tool and sheet metal contact are extremely important. In addition to fracture depth, which is a main investigation indicator, the paper also presents more complex parameters for estimation of contact conditions influence – fracture force and realized strains distribution, as well as relations in forming limit diagram. Furthermore, it shows that in the multistage forming conditions, i.e. at modification of so called strain paths, contact conditions have a considerable influence on the degree of realized limit strains. Steel and Al-alloys sheet metals were used in the experiment. In addition to the analysis from the formability aspect, the specified methodology can be used with great success for the estimation of technological qualities of lubricants for deep drawing.Publishe

Numerical modeling of ironing process

Based on comprehensive experimental research and physical modeling of ironing, and detailed study of the material characteristics of the work piece and tool, as well as investigation of the contact friction conditions and measuring temperature generated by this contact friction, we were able to conduct a set of "numerical experiments" using finite element method implemented in the software Simufact.forming. The goal of numerical modeling was to use 3D visualization of the process, especially in deformation zone, to present strain, stress, velocity, and temperature fields which will enable more detailed analysis of the physics of the process. For that purpose a nonlinear FE approach is applied, using solid 3D finite elements, which are optimized for metal forming simulations. This allows obtaining accurate simulation results with the evaluation of changes in the sheet thickness, the effects of residual stress and recurrent elastic strains. Numerical modeling of the process, as well as results of FE analysis have allowed us to obtain important information about the ironing process such as the stress at the wall, strains, deformation forces, generation of temperature in the work piece as a result of plastic strains and the influence of contact friction and transfer of this temperature it to the die. All of these output parameters are evaluated depending on the angle of the die, the forces on the holder, lubrication conditions and the strain rate, analogous to the plan of experiments in physical modeling.Publishe

Wetting phenomena of grooves at liquid metal/ceramics interface

The grain boundary groove (GBG) developing at the ceramic substrate under the liquid metal is evident, yet not fully explained influencing appearance in describing the wetting phenomena at liquid metal/ceramics interface. The focus here is on modeling of the phenomena at/around a groove between grains depending on grooves’ geometry. Based on atomic force microscopy results, the groove efficiency assessment is provided as a function of the transferred mass quantity and related to grooves geometry. The transferred mass quantity and, according to it, the groove efficiency at parabolic GBG is about 10 % higher comparing to the triangular GBG

The investigation of applicability of the Hollomon-Jaffe equation on tempering the HSLA steel

High strength low-alloyed (HSLA) Cr-Mn-Si steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Those properties depend both on the temperature and time of tempering. Knowing the tempering parameters, it is possible to reach the desired properties of the treated steel. Some results on investigating the Hollomon-Jaffe equation (in parametric form) application for tempering of HSLA steel, are shown in this paper. The experiments were performed in real production conditions, using a standard material. The quenching was performed at 870 C, the heating period was always 30 min, with subsequent cooling into the oil bath. The tempering was carried out in temperature range from 480 to 680 C, while tempering time varied from 15 min to 24 h. The degree of tempering is referred through the hardness values changing. The experimental results have shown a pretty well agreement to tempering parameters, included in Hollomon- -Jaffe equation, for this kind of HSLA steel