THE LASER USER


ISSUE 114 AUTUMN 2024 LASER WELDING


100 Hz) was 206 N/mm, which was improved by about 10% by Zn removal in ID2, while the comparison between ID 3 and ID 4 (150 Hz) shows nearly 50% improvement. The correlation between joint strength and connection area is 0.99, demonstrating a clear relationship.


Conclusions


Figure 3: (a) Cross-section and EDS results (the red area) of the samples with (ID 1) and without Zn coating (ID 2), and (b) thickness of the total IMC and Fe2


Al5 phase.


This paper examines the effect of Zn coating during remote laser welding of Zn-coated steel to aluminium in a nominal zero part-to-part gap lap configuration. Zn coating was removed in half of the samples during the first pass to assess its impact on weld strength and process repeatability. Welds were then produced in the second pass. The presence of Zn coating resulted in a smaller, uneven connection area between steel and aluminium due to localised explosions that inhibited melting of the aluminium sheet. Zn vapours destabilised the molten pool, increasing the average thickness and variation of intermetallic compounds. It was observed that joint efficiency reached up to 72% when the Zn coating was removed, compared to 65% with the coating present. Joint strength showed a strong correlation with the connection area (Pearson’s correlation of 0.99).


Acknowledgements


This work was supported by EPSRC JLR iCase voucher 20000095 (Remote Laser Welding of Dissimilar Metals for Automotive Structural Applications).


References


[1] A. Gullino et al. ‘Review of Aluminum-To-Steel Welding Technologies for Car-Body Applications’, 2019, doi: 10.3390/MET9030315.


[2] S. Kuryntsev, ‘A Review: Laser Welding of Dissimilar Materials (Al/Fe, Al/Ti, Al/Cu)— Methods and Techniques, Microstructure and Properties’, 2021, doi: 10.3390/MA15010122.


Figure 4: Lap shear tensile test results for the samples with (ID 1 & 3) and without Zn coating (ID 2 & 4).


mixing in Zn-coated samples, with various intermetallic compounds (IMCs) identified at the joint edge, where mixing is most intense. Thicker IMC layers result from increased interaction between iron (Fe) and aluminium (Al) atoms, raising susceptibility to cracking. Figure 3b shows the thickness of total IMCs and the brittle Fe2


Al5


phase, revealing that Zn-coated samples exhibit greater total IMC thickness and variability due to differing penetration depths and mixing levels.


Lap shear tensile results are shown in Figure 4. The average linear load is higher for samples without Zn coating, with less variability indicating greater repeatability. This can be linked to the topographic and microstructural properties observed (Figures 2 and 3(a)). Zn-coated samples (ID 1 and 3) exhibit less connection area, resulting in weaker joints. The broad variability in joint strength for these samples is due to


unstable molten pool behaviour, leading to uneven connection areas and localised mixing, as reflected in the total IMC thickness (Figure 3(b)).


Linear load is higher at 100 Hz for both conditions, attributed to the larger connection area compared to the inadequate penetration at higher frequencies. The highest average linear load of 225 N/mm was achieved in the uncoated sample (ID 2, 100 Hz), yielding 72% joint efficiency against the weakest parent material (5251-H22 aluminium with a UTS of 315 N/mm). The highest load in the Zn-coated sample (ID 1,


[3] https://www.youtube.com/ watch?v=XpCFjREj4hg


An extended version of this study is published in Procedia CIRP, 124: 678-683 (2024), https://doi.org/10.1016/j.procir.2024.08.200


*P. Franciosa, S. Jabar, D. Ceglarek (U. Warwick), H.R. Kotadia (Liverpool John Moores University), K.F. Ayarkwa, J.R. Smith (Jaguar Land Rover)


Contact: Ali Baghbani Barenji Ali.Baghbani-Barenji@warwick.ac.uk https://bit.ly/wmg_laserbeamwelding


Ali Baghbani Barenji is a PhD student at WMG, University of Warwick. His work focuses on laser welding and the corrosion of dissimilar steel to Al parts.


SEE OBSERVATIONS P26 21


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36