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Chemical joining of aluminum to steel parts is one of the main challenges in the automotive industry to achieve sound economical solutions for required automobile weight reduction. The cold metal transfer (CMT) is a fusion welding process developed to meet that challenge. It is shown in this paper how the choice of proper filler materials can yield appropriate mechanical performance of specially designed dissimilar CMT butt joints by improving the seam characteristics and weld bead properties.

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Abstract. Structure formation upon 500 fs 248 nm KrFlaser irradiation of PolyEthylene Terephthalate (PET) and Polylmide (PI) has been investigated. The results obtained with fs pulses have been compared to those with ns pulses. 42.55, 81.40, 82.65 Irradiation of polymers with pulsed UV-laser light and pulse lengths of, typically, 1-50 ns frequently results in surface-structure formation [1][2][3]. These structures are often periodic or quasi-periodic in the sense that either the one-or two-dimensional lateral Fourier transform of the structure height h (x, y) corresponds to a single frequency or a relative narrow group of frequencies, respectively. The structures can be classified according to two groups: coherent and non-coherent structures. PACS:Coherent laser-induced surface structures such as ripples and dots are due to interference between the incident laser light and surface-scattered waves [4,5]. The periodicity of such structures is of the order of the wavelength of the light and depends on the angle of incidence of the laserbeam. Ripple formation has been observed on various polymers, including Polylmide (PI) and PolyEthylene Terephthalate (PET), at laser fluences below [6-8] and above [9 11] the ablation threshold ~th" On PI, coherent structures with linewidths below 100 nm have also been obtained by means of an excimerlaser interference technique [11][12][13].Non-coherent structures with a periodicity in the micrometer range are frequently observed in polymers. These structures are either regular spaced naps, or joining or branching walls with a preferred direction (similar to Fig. 1). For uniaxially and biaxially stretched foils wall-and nap-type structures, respectively, have been observed [14][15][16][17]. The internal stress-fields are related to either the production process of the polymer foil itself or/and to post-fabrication stretching.Non-periodic microstructures on excimer-laser irradiated PET have been reported in [18]. These structures consist of branched dendrites that have a lateral dimension in the micrometer range and a height of 5-30 nm.Femtosecond UV excimer-laser ablation was investigated for polymers [19][20][21], LiNbO3 [22], superconductors [23], and fused silica [24]. Ultra-short pulses require lower threshold fluences for ablation than ns pulses and yield an improved surface quality within the ablated areas.In this paper we study the formation of structures induced by femtosecond excimer-laser pulses on polymer surfaces.