JOINING OF METALLIC COMPOSITE MATERIALS BY CMT PULSE

Transcription

1 JOINING OF METALLIC COMPOSITE MATERIALS BY CMT PULSE Mihaela POPESCU a, Radu Alexandru ROŞU a,cosmin LOCOVEI a, Ion Aurel PERIANU a a Politehnica University of Timişoara, Faculty of Mechanical Engineering, Bd. Mihai Viteazu Nr.1, Timişoara, Romania, mihaela.popescu@mec.upt.ro Abstract Composite materials are specifically designed to respond to particular requirements in terms of mechanical strength and stiffness, corrosion resistance, resistance to chemical agents, low weight, dimensional stability, resistance to shock, wear properties, insulating and aesthetic, features which recommends this materials to be used in top fields of engineering (aeronautic, biomedical, etc). These advanced materials present also an economic benefit, having a low weight together with high strength at high temperatures. Realization of these composites materials and joining them shows a high degree of complexity by combining aspects of material properties, functional needs, and a practical multifunctional development. The paper presents experimental data by joining with CMT process (Cold Metal Transfer) of metal matrix composites (aluminum) reinforced with steel mesh S235JR. The microscopic analyzes performed with optical microscopy and scanning electron microscopy presented not welding defects. It also notes that were not been seen defects after examination in the cross-section of the composite material. The estimator values Δ determined between the areas base metal - weld of the joints shows that did not appeared structural hardening (Δ<50%), which attest that will not appear important structural hardening, the risk of breaking fragile in these areas being considered low. Keywords: composite materials, CMT welding, microscopic analysis 1. INTRODUCTION Composite materials are part of "new materials" and are specifically designed to respond to particular requirements in terms of: mechanical strength and stiffness, corrosion resistance, resistance to chemical agents, low weight, dimensional stability, resistance to variable demands to shock and wear, insulation and aesthetic properties. Of all the new materials, composite materials are characterized mostly by strong interdisciplinary scientific and industrial applications [1]. In the particular case of vehicles, there are made now parts from composite materials but is still expected to generalize this replacement because the economic factor is very important. Thus, to manufacture structural elements of a car (chassis bodyshell, transmission shafts) of high performance composite materials (polymer matrix and C fiber) the gain realized in fuel economy is important [2]. Welding of composite materials by conventional methods may lead to inappropriate welded joints due to the large differences between materials reinforcement elements and matrix material that, when using high temperatures can lead to deformation or cracking [3,4]. CMT joining process (Cold Metal Transfer) is experiencing a growing application in various industries (aviation, maritime, auto etc.) due to advantages compared to other welding processes namely: temperature during welding is approximately 30% lower than the temperature released during the MIG-MAG welding, computer assisted sequencing joining process will produce high-quality welded joints with minimum material consumption (no drops) [5,6]. With CMT process can be made high quality joints of similar and dissimilar materials (aluminum alloy, zinc alloy, aluminum alloy, magnesium alloy, aluminum alloy galvanized sheet etc.) of small plates with

2 thicknesses between mm. Applying CMT joining method, due to the lower heat than conventional methods are expected to obtain quality welded joints without cracks or deformation due to lower stress [7]. The paper presents experimental results on composite materials joining Silumin 3 reinforced with S235JR steel mesh by CMT method. 2. MATERIALS USED 2.1 Matrix material (Silumin 3) was prepared in low frequency induction furnace. Its chemical composition is shown in Table 1. In table 2 is presented the chemical composition of the steel mesh Tab. 1 Matrix chemical composition Al Si Mn Mg Fe Ti Zn Cu 89,6 87% 10 12% 0,3 0,6% 0,2 0,5% 0,6% 0,15% 0,10% 0,05%. Tab. 2 Chemical composition of the steel mesh Fe C Mn Si P S 99,32 98,73% 0,13 0,22% 0,3 0,6% 0,15 0,35% 0,045% 0,055% 2.2 Filler material As filler material was used AlMg5 wire electrode with the diameter of 1.2 mm. Table 3 presents the chemical composition of the wire electrode and in Table 4 are listed the mechanical properties of the filler alloy. Tab. 3 Chemical composition of the wire electrode Filler material Chemical composition [%] C Mn Si Cr Zn Ti Mg Fe Al AlMg rest Tab. 4 Mechanical properties of the filler alloy Tensile Strength Filler material N/mm 2 AlMg5 Yield Strength N/mm Elongation A5 (%) Equipment used For the experimental program was used the welding power source type Fronius TPS 2700 CMT which is controlled by microprocessor, designed for MIG-MAG/CMT welding processes. Was also used a welding tractor which provides the advanced. It has a voltage regulator to determine the welding speed, continuously adjustable. Figure 1 shows the CMT system used.

3 Fig. 1 Experimental equipment As shielding gas was used argon purely (Ar 100%) because for aluminum and copper alloys is recommended that inert gas welding. Table 5 presents the optimal values of the parameters used to achieve joints. Tab. 5 Values of the parameters Wire speed I S A U a V m/min Impedance [Ω] Gas l/min Equipment used for investigation of the joints Microstructural analysis was performed using OPTIK OLYMPUS BX51 microscope. The samples etching for examination was done with hydrofluoric acid, 1% at 20 for 10 seconds. Scanning electron analysis was performed using scanning electron microscope (SEM) inspection model coupled with the Energy-dispersive X-ray spectroscopy (EDX). HV0.1 hardness tests were made with ZWICK 3212 device. 3. EXPERIMENTAL RESULTS 3.1 Microscopic analysis Figure 2 presents optical microscope metallographic analysis of the base metal 1 (Silumin 3). Fig. 2 Microstructure Silumin 3 alloy, 200x

4 In Figure 3 is presented the joint microcopy image produced by CMT (interface). Fig. 3 Joint image (interface), 500x The microscopic analysis shows that the welded joints presents not defects such as pores. It also notes that between the two materials there is a good contact without cracks. In Figure 4 is presented SEM analysis of the composite (cross section). a) b) Fig. 4 SEM analysis of the composite (cross section): a) 200x, b) 800x

5 SEM analysis shows that the reinforcing material (S325JR steel mesh) is well integrated in the aluminum alloy matrix. 4. HARDNESS TEST HV0.1 hardness test was performed according to EN ISO :2005. Specific areas of the joints and the results are summarized in table 6. Also in Table 6 were introduced the structural hardening estimator ΔHV0.1 values calculated with the formula: Δ = max max min 100 [%] Where: max is the maximum hardness in an area of the joint; min is the minimum hardness determined in a different area of the joint It is considered that if ΔHV0.1 50% in areas considered were developed hardening-embrittlement phenomena exacerbated by structural, high-risk breaking fragile production [8]. Tab. 6 hardness test Area Hardness Estimator Δ [%] BM 1 -WELD BM 2 -WELD BM 1 34,4 WELD BM 2 36 Analyzing ΔHV0.1 estimator values determined in the specific areas of the joints is observed that there is no structural hardening trends between areas BM 1 -WELD, BM 2 -WELD attesting that no major structural hardening occurs (Δ <50%), risk of breaking fragile in these areas is considered low. ACKNOWLEDGEMENT This work was partially supported by the strategic grant POSDRU/89/1.5/S/57649, Project ID (PERFORM-ERA),co-financed by the European Social Fund Investing in People, within the Sectoral Operational Programme Human Resources Development CONCLUSIONS 1. The paper presents experimental results of joining metal matrix composites (aluminum) and reinforced with steel mesh S235JR, joined by CMT. 2. Microscopic analysis shows that the joints made are appropriate and without defects such as pores or cracks. SEM analysis of the composite (cross section) shows that the reinforced material (S325JR steel mesh) is well-integrated in the aluminum alloy matrix 3. Δ estimator values determined in the specific areas of the joints is below 50% which shows that there were no major structural hardening which may lead to fragile breaking.

6 LITERATURE [1] BELU-NICA R., ROŞU R., POPESCU M., CZIPLE F., PERIANU I. Problems in the Preparation and Processing of Composite Materials Type Silumin 3 - Reinforced Matrix with S235JR Steel Mesh, October 16 th 18 th NANOCON 2012 [2] ZHENYANG L, HUANG P. ARC welding method for bonding steel with aluminum, Mechanical Engineers, vol. 4, pp , 2009 [3] BORRISUTTHEKUL, R. MITSOMWANG P. Feasibility of Using TIG Welding in Dissimilar Metals between Steel/Aluminum Alloy, Energy Research Journal, 2010, vol. 1(2) pp [4] TROMMER, G. CMT und Impulslichtbogen prozess allein und in Kombination fur einem erweitern Lichtungsbereich, Der Praktiker, 2008,vol.10, pp [5] CHOVET, C., GUIHEUX, S. Possibilities offered by MIG and TIG brazing of galvanized ultra high strength steels for automotive applications, La Metalurgia Italiana, 2006, Vol.54, No.7-8, pp [6] FORTAIN, J.M., RIMANO, L., VAIDYA, V. Innovative Process Improves Welding of Sheet Metal Parts, Welding Journal, 2008, Vol.87, No.1, pp [7] POPESCU, M., MARTA, C., MAGDA, A., VOICU, A., LOCOVEI, C., DUPŢA, A. Thermal Coatings and Reconditioning. Experimental themes, Politehnica Publishing House, Timişoara, 2008 [8] SAFTA I. V. Technological tests of the welded joints, Publishing House Sudura, 2006, Timişoara, România