## 1 Introduction  
Metal matrix composites are increasingly used as construction materials due to their special mechanical properties [1, 2, 3]. Cast aluminium alloy-based composites [4, 5, 6] reinforced with ceramic material in the form of long fibres [7, 8], short fibres [9, 10] and particles [11, 12] account for a significant share of this application. In addition to the many advantages conditioning their use, they are characterised by certain disadvantages, which primarily include the difficulty of joining structural elements using welding methods [13, 14, 15]. The mechanical properties and structural structure of joints of aluminium alloy matrix composites in friction welding [16, 17] and friction stir welding [18, 19, 20] have been widely described in the literature. During welding with the above-mentioned methods, material melting and re-solidification do not occur, which minimises the surface reactions at the reinforcing phase-metal matrix interface. Despite its undoubted advantages, friction welding has limitations in terms of the shape of the parts to be joined. One of the basic welding techniques is the TIG (Tungsten Inert Gas) method, which is relatively inexpensive and allows the joining of parts of varying shapes [21, 22, 23]. The application of the TIG method for joining aluminium composites reinforced with ceramic particles involves melting the metal matrix and re-solidification of the liquid weld pool. The manner of crystallisation of the matrix alloy and the influence of the crystallisation front on the distribution of the reinforcing phase, wettability and the product of surface reactions at the liquid metal-ceramic phase interface have a significant impact on the mechanical properties of the weld. Typically, welded microstructures are characterised by a dendritic structure with an uneven distribution of the reinforcing phase in the interdendritic spaces [24; 25; 26; 27; 28]. In the case of metal-ceramic composites, the factor of the physical and chemical interactions that occur between the liquid metal and the ceramic reinforcing phase must additionally be considered [29; 30; 31]. The durability of the bond between the liquid and solid phase depends on the surface tension of the liquid and the contact angle, which determines wettability. For aluminium-silicon ceramic systems, the contact angle exceeds 90\({}^{\circ}\) and, in most cases, even 120\({}^{\circ}\). Hence, it follows that the work of adhesion in such systems has a low value, which is detrimental to the mechanical properties of the composites [32; 33]. One possibility for improving the metal-ceramic interface is to introduce chemical elements into the liquid metal that improve the wettability of the reinforcing phase by reducing the surface tension, lowering the surface energy of the liquid at the liquid-solid interface or forming chemical compounds that improve wettability [34; 35]. Many of the aluminium alloys exhibit a tendency for hot cracking during the welding process. The applied heat energy and the associated temperature distribution in the welded joint area results in internal stresses and microstructural changes in the re-solidified weld and zones with partial melting of the material [36]. Internal stresses leading to open hot cracks result from two consecutive processes: the expansion of the metal under the influence of the supplied heat energy and the significant contraction of the metal during crystallization [37]. The second type of damage occurring in the heat-affected zone is the so-called liquid cracking, created by the presence of a film of liquid metal with a low melting point at the grain boundary. As stated by [PERSON] and [PERSON] [38; 39], liquid cracking in the HAZ depends on the stability and solubility limit in the \(\alpha\)-phase of the liquid-initiating particles of the precipitates formed during the fabrication process. Sub-melts appear at the phase boundaries, after which they solidify in the form of eutectics.