Electron Beam Welding of Die Cast Aluminum Alloy

Electron Beam Welding of Die. Cast Aluminum Alloy components for Automotive Industry by Frantisek KOLENIC First Welding Company, Bratislava Slovak Republic E-mail: kolenic. frantisek@pzvar. sk First Welding Company Frantisek Kolenic 1

Content of the presentation n n n n 1. Introduction of the First Welding Company 2. Analysis of the welding problem 3. Requirements for welded joint 4. Selection of welding method 5. Welding technology 6. Welding equipments for mass production 7. EB welding of heat exchangers for trucks Conclusions First Welding Company Frantisek Kolenic 2

PRVÁ ZVÁRAČSKÁ, a. s. (First Welding Company, Inc. ) n n n Type of company: Research, Production, Consultancy, SME. Founded in 2001. Number of employees: 86. Main activities: n R&D – laser, electron beam and plasma welding and allied technologies for industrial use, High production arc welding technologies. n Products – Electron beam welding equipment, Single-purpose welding equipment, Vibration equipment for residual stress reduction, Development of the welding technologies. n Services - Electron beam welding and surfacing, Laser processing of materials (welding, quenching, cutting, surfacing), Plasma cutting, Soldering. n Comprehensive services in repair of power engineering parts. n Expertise activities – in the field of welding technologies, welded constructions. n Certification – personnel in welding and NDT. First Welding Company Frantisek Kolenic 3

Introduction n n Welding of die-cast aluminum alloy components is a complex problem. In industrial praxis we can find sufficient demands for such welding. One of the examples are heat exchangers of independent heating and cooling of passenger’s cars and trucks. Due to the complicated shape of the main body they can not be dye casted in one step. They usually consist of two or more die-casted parts which must be tightly connected by welding. First Welding Company Frantisek Kolenic 4

Analysis of the problem Problems of welding of dye casted aluminum alloys by high energy density sources may be in general characterized by the following way: n n n Occurrence of surface layer of aluminium oxide, high thermal conductivity of parent metal, high thermal expansivity coefficient, wide interval of alloy solidification, hydrogen content in alloy. First Welding Company Frantisek Kolenic 5

Requirements for welded joint n n Smooth surface formation of the weld bead without excess over the welded surface and fall-through below this surface down to 0. 2 mm, minimum 2 mm penetration depth, vacuum tight joint with minimum porosity, less than 0. 2 % spoiled welds. First Welding Company Frantisek Kolenic 6

Entry conditions n n Positive The aluminium alloy Al. Si 10 with conventional 10 % Si and other admixtures on max. 0. 5 % level with total Al 88. 6 % content represents a typical alloy for die casting. It is characterised especially by very good penetration, tightness and resistance to hot crack formation. From the viewpoint of weldability higher Si content in the alloy is favourable especially if filler metal is not used. First Welding Company Frantisek Kolenic 7

Entry conditions n n n Negative: Different width of welding gap (0 -0, 8 mm), cleaning is done only by washing in ecological solutions which do not assure perfect purity of weld edges and the weld edges are not otherwise cleaned either mechanically or electrolytically, surface layer of aluminium oxides, which is formed immediately at contact with the air exhibits porous character and hence it can contain water vapours from the air. If it is not removed it can induce especially pore and crack formation in the weld, the time between production of weldments and the time of welding differs from 1 day up to 10 weeks, in some castings pores and other defects are present near the weld edge. Those can be opened during welding. First Welding Company Frantisek Kolenic 8

Selection of welding method Laser Electron beam Welding equipment CO 2 laser – fast axial flow 5 k. W – Mod TEMoo EB machine VUZ EZ 1000 6 k. W Welding power k. W 3, 2 0, 75 – 1, 4 Accelerating voltage k. V 42 Welding current m. A 10 up to 32 Welding speed mm. s-1 20 up to 60 Rotary beam motion Ø mm 0, 2 Frequency k. Hz 7, 5 Focus 1 mm below the surface Active gas and its pressure Pa Ar Number of passes 1 up to 4 First Welding Company Frantisek Kolenic On the surface 1 up to 4 9

Examination of the weld properties n n The examination of the weld properties have been done as follows: - the specimens were cut by cross cuts (2 cuts from each weld) on which the structure was examined metallographically, - the specimens 10 mm in length have been cut along the central axis of the weld. The number and size of pores was analysed on prepared surfaces at 20 fold magnification. The number and size of pores was studied in dependence on welding speed and the number of passes for laser beam and electron beam welding processes. - micro cracks were studied on macro etches metallographically. First Welding Company Frantisek Kolenic 10

Experimental Results-Laser Welding macrographs The first run The second run The third run The fourth run First Welding Company Frantisek Kolenic 11

Experimental Results-EB Welding macrographs The first run The second run The third run The fourth run First Welding Company Frantisek Kolenic 12

Experimental Results-Laser Welding First Welding Company Frantisek Kolenic 13

Weld bead formation using electron beam technology First Welding Company Experimental Results-EB Welding macrographs. 14

Results of the experiments n n n The results have proved that the size and number of pores in laser beam welding is in principle higher than in electron beam welding. In laser beam welding the number and size of pores only little changes with welding speed and with the number of passes. It seems that the smaller pores only agglomerate into larger pores with increasing number of passes. In electron beam welding on the contrary to laser beam welding the susceptibility to pore formation is expressively decreased with increasing number of passes. Pore formation is eliminated at three - four passes. The results have clearly proved better suitability of electron beam welding. This might be due to vacuum where the escape of gases from the weld is supported by low pressure. On the contrary in laser beam welding the pressure of shielding gas on the surface of weld pool acts contrarily whereas also the humidity of the atmosphere can enhance pore formation. First Welding Company Frantisek Kolenic 15

Welding Equipments for Mass Production n n n n For mass production welding of aluminium heat exchangers two single-purpose welding have been developed. Both equipments consist of the same welding source, electron beam gun and auxiliary sources with the following characteristics: Accelerating voltage 30 – 60 k. V Max. power 6 k. W Ripple of acc. Voltage ± 1, 5 % Max. deflection of the beam ± 7° Beam oscilation frequency 0 – 10 k. Hz Electron beam gun triode with La. B 6 cathode First Welding Company Frantisek Kolenic 16

High Production Electron Beam Welding Machine EB ZH-2 First Welding Company Frantisek Kolenic. 17

High Production Electron Beam Welding Machine EB ZH-2 First Welding Company Frantisek Kolenic 18

Conclusions n n In the selection process of welding technology laser and electron beam welding processes were verified. From the viewpoint of porosity and bead formation electron beam welding has unambiguously been proved as more convenient. In service of welding equipments with two concepts of handling of weldments the concept at which the weldments are transferred from the magazine chambers in the welding chamber with the whole magazine in the number of 8 pcs has been proved as more convenient. Vacuum-tight welded joints without inhomogeneities were fabricated by employing electron beam welding with the technique of multiple passes of electron beam welding. Different welding parameters were applied for individual passes assuring the full penetration of welded joint. The last pass of the beam was destined for achieving a uniform surface formation of the weld bead. First Welding Company Frantisek Kolenic 19