A SIMILAR and DISSIMILAR LAP JOINTS by CO 2 LASER WELDING of DIFFERENT FAMILY Al ALLOYS G. Daurelio , E.S. Andriani , I.M. Catalano InterAteneo Physics Department “ M. Merlin “ of the University and Polytechnic of Bari Bari, Italy . 21 - 22 May 2009 VENEZIA - ITALY EUROJOIN 7 G N S 5 Contacts : daurelio@fisica.uniba.it ABSTRACT This work presents the experimental results obtained on laser welding of different aluminium alloys as AA1090 (series 1000), AA5059, 5083 and 5383 (series 5000 Al - Mg) and 6082 (6000 series Al - Mg - Si). These Al alloys are very attractive for manufacturing sectors of aviation, automobile, rail and maritime, especially for high-speed trains and ferries for high-speed (HSLC - High Speed Light Craft). Using these materials were carried out experiments aimed at obtaining joints between similar and dissimilar alloys in different thickness. The thicknesses of the plates in question are in the range 1 to 3 mm and thickness of the joints varies from 2 to 5 millimetres. The source used was a CO2 laser of ROFIN SINAR, type RS 25 and the range of the used laser powers varied between 1 and 2.5 kW. Welding speeds were tested between 10 and 150 mm / s. The joints, which were considered the best ones after a first evaluation to the stereo-microscope as for the roots as for the crown beads, were cut transversely and subjected to usual working metallographic examinations . Later some tests by using a stereo microscope, interfaced to a system computerized image analysis (LUCIA of NIKON - LIM 4.82 type ) to capture, store and measure the usual parameters melted area of the bead in cross section, were carried out. Followed careful assessments of both metallurgical and structural nature, in the light of the different alloys of Al, similar or dissimilar, used to form the joint. A careful evaluation was conducted to study the influence of the alloy input to the laser beam than to come in below overlap on the structure and final melt of the joint . Finally a numerical evaluation of the all chosen joints has been applied to evaluate the laser welding efficiency parameter. CONCLUSIONS The MAX WELDABLE THICKNESS is in the ORDER OF a FACTOR 1. 5 to 2 of the EMPLOYED POWER (a Laser from 5 to 6 kW will not succeed to weld "well" more than one thickness of 7. 5 to 10 mm) It is NECESSARY NOT TO USE LASER POWER LEVELS HIGHER THAN 5 to 6 kW AS THEY GROW MUCH MORE the SUPERFICIAL AND INNER DEFECTIVE STATE of the BEAD as well as the POSSIBILITY of HOT – CRACKS AA 5083 has indicated that the values of defocusing BETTER are Z = 0 and Z = + 2 The AA 6082 and AA 1090 SHOW the SIMILAR BEHAVIORS for the LASER WELDING, PREFERRING SAME DEFOCUSING conditions (Z = 0 and Z = +2) The WELDING of the Al-Mg ALLOYS shows on the crown an evident effect of the EVAPORATION of the Mg from the FUSED BATH, and it is characterized by incomplete or less depths than other Al Alloys The VALUES OF WELDING SPEED DO NOT GROW MORE when power level higher than 6 kW has used , to parity of thickness and of the other experimental CONDITIONS THREE ALLOYS AA 5083, AA 5383, AA 5059, DENOTE IDENTICAL BEHAVIOURAL TENDENCY PREFERRING THE HIGH WELDING SPEEDS SO THAT THEY ALLOW THE REDUCTION OF THE SUPERFICIAL DEFECTIVE STATE The WELDING between Dissimilar Al Alloys AA 1090 - 5xxx or 6xxx , in the CASE of the Al - Mg ALLOYS, THEY EVIDENCE A REGULAR BEAD, probably due to a such "CALMING" EFFECT in the fused BATH tooled from the ALUMINUM The BEST BEADS OBSERVED HAVE BEEN REALIZED BY AN ALLOY AA 6082 The VALUES of the ASPECT RATIO found EVIDENCE CLEARLY THAT IT HAS BEEN OPERATED IN REGIME of Key-hole CONCLUSIONS for the WELDING EFFICIENCY - WE – according to the DA.LU. Model and WE “ Dau Unit “ ( mm 3 / k J ) For the Aluminium and its alloys (Series 1000, 2000, 4000, 5000, 6000, 7000 and 8000), even if the data examined are still many meager (less than 60), since at the moment exist remarkable difficulties to obtain good weldings to laser of these alloys with sources laser, seem reasonable to assume that the efficiency of the welding to laser of this metal and of its alloys turns out to be always the much highest one ( from 78 to 100 Dau ) of found how much on all the stainless steels over examine ( from 30 to 50 Dau) : they are similar or quite higher than those measured for titanium alloys. At the moment it appears not useful to indicate values of Dau for the three intervals, being wished to attend a number more meaningful than given. They are available data experiences them on alloys AA1090, 1100, 2024, 5053, 5056, 5059, 5383, 6061, 6063, 6082, 8090. Plasma Colour during the Laser Welding : GREEN COLOUR On the light of the above cited Dau units for Al Alloys, it was to be expected values of WE comparable to the Cu and its alloys ones but not quite higher than those obtained on the Stainless steel and even of Ti Alloys . Therefore the WELDING PROCESS by LASER of Al and its ALLOYS has not fully still understood . Perhaps it will be just the DA.LU. Model and the Dau Unit to supply of the ulterior possible explanations on the interaction Laser – Matter, in the field of Al Alloys , so that at the end to solve the PROBLEM to WELD well by LASER the Al Alloys without added filler material as well as the employing Hybrid Laser Systems . Plasma Colour during the Laser Welding : ROSE COLOUR 1