**2. Material and methodology**

The investigation was carried out on the AlCu4Ni2Mg2 and AlSi5Cu1Mg casting aluminium alloys. The chemical composition of the alloys is indicated in Table 1.


Table 1. Chemical composition of investigated AlCu4Ni2Mg2 and AlSi5Cu1Mg aluminium alloys, Al bal (wt%)

Microstructure analysis was carried out on the as-cast and in T6 condition aluminium alloys. The alloys were subjected to T6 heat treatment: solution heat treated at 520°C for 5 h followed by water cooling and aging at 250°C for 5 h followed by air cooling. The

and/or impurities. In the aluminium alloys besides the alloying elements, transition metals such as Fe, Mn and Cr are always present. Even small amount of these impurities causes the formation of a new phase component. The exact composition of an alloy and the casting condition will directly influence the amount and type of intermetallic phases (Dobrzański at al., 2007; Warmuzek at al. 2004, Zając at al., 2002). Depending on the composition, a material may contain CuAl2, Mg2Si, CuMgAl2, and Si as well as Al(Fe,M)Si particles, where M denotes such elements as Mn, V, Cr, Mo, W or Cu. During homogenization or annealing, most of the as-cast soluble particles from the major alloying additions such as Mg, Si and Cu dissolve in the matrix and they form intermediate-sized 0.1 to l μm dispersoids of the AlCuMgSi type. Dispersoids can also result from the precipitation of Mn-, Cr-, or Zrcontaining phases. A size and distribution of these various dispersoids depend on the time and temperature of the homogenization and/or annealing processes. Fine intermetallic particles (<l μm) form during artificial aging of alloys and they are more uniformly distributed than constituent particles or dispersoids. Dimensions, shape and distribution of these particles may have also important influence on the ductility of the alloys. Therefore, a systematic research is necessary regarding their formation, structure and composition. For example, the coarse particles can have a significant influence on a recrystallization process, fracture, surface and corrosion, while the dispersoids control grain size and provide stability to the metallurgical structure. Dispersoids can also have a large affect on the fracture performance and may limit strain localization during deformation. The formation of particles drains solute from the matrix and, consequently, changes the mechanical properties of the material. This is particularly relevant to the heat-treatable alloys, where depletion in Cu, Mg, and Si can significantly change the metastable precipitation processes and age hardenability of the material (Garcia-Hinojosa at al., 2003; Gupta at al., 2001; Sato at al., 1985). Therefore, the particle characterization is essential not only for choosing the best processing routes, but also for designing the optimized alloy composition (Mrówka-

Nowotnik at al., 2007; Wierzbińska at al., 208, Zajac at al., 2002; Zhen at al., 1998).

techniques for analysis of the intermetallic phases occurring in the aluminium alloys.

aluminium alloys. The chemical composition of the alloys is indicated in Table 1.

**2. Material and methodology** 

alloys, Al bal (wt%)

The main objective of this study was to analyze a morphology and composition of the complex microstructure of intermetallic phases in AlSi5Cu1Mg and AlCu4Ni2Mg2 aluminium alloys in as-cast and T6 condition and recommend accordingly, the best experimental

The investigation was carried out on the AlCu4Ni2Mg2 and AlSi5Cu1Mg casting

**Alloy Cu Mg Si Fe Ni Zn Ti AlSi5Cu1Mg** 1.3 0.5 5.2 0.2 - <0.3 0.18 **AlCu4Ni2Mg2** 4.3 1.5 0.1 0.1 2.1 0.3 - Table 1. Chemical composition of investigated AlCu4Ni2Mg2 and AlSi5Cu1Mg aluminium

Microstructure analysis was carried out on the as-cast and in T6 condition aluminium alloys. The alloys were subjected to T6 heat treatment: solution heat treated at 520°C for 5 h followed by water cooling and aging at 250°C for 5 h followed by air cooling. The microstructure of examined alloy was observed using an optical microscope on the polished sections etched in Keller solution (0.5 % HF in 50ml H2O). The observation of specimens morphology was performed on a scanning electron microscope (SEM), operating at 6-10 kV in a conventional back-scattered electron mode and a transmission electron microscopes (TEM) operated at 120, 180 and 200kV. The thin foils were prepared by the electrochemical polishing in: 260 ml CH3OH + 35 ml glycerol + 5 ml HClO4. The chemical composition of the intermetallics was made by energy dispersive spectroscopy (EDS) attached to the SEM.

The intermetallic particles from investigated AlCu4Ni2Mg2 and AlSi5Cu1Mg alloys in T6 condition were extracted chemically in phenol. The samples in the form of disc were cut out from the rods of ∅12 mm diameter. Then ~0.8 mm thick discs were prepared by two-sided grinding to a final thickness of approximately 0.35 mm. The isolation of phases was performed according to following procedure: 1.625 g of the sample to be dissolved was placed in a 300 ml flask containing 120 mm of boiling phenol (182°C). The process continued until the complete dissolution of the sample occurred ~10 min. The phenolic solution containing the residue was treated with 100 ml benzyl alcohol and cooled to the room temperature. The residue was separated by centrifuging a couple of times in benzyle alcohol and then twice more in the methanol. The dried residue was refined in the mortar. After sieving of residue ~0.2 g isolate was obtained. The intermetallic particles from the powder extract were identified by using X-ray diffraction analysis. The X-ray diffraction analysis of the powder was performed using a diffractometer - Cu Kα radiation at 40kV.

DSC measurements were performed using a calorimeter with a sample weight of approximately 80-90 mg. Temperature scans were made from room temperature ~25°C to 800°C with constants heating rates of 5°C in a dynamic argon atmosphere. The heat effects associated with the transformation (dissolution/precipitation) reactions were obtained by subtracting a super purity Al baseline run and recorded.
