Annealing Effects in Cast Commercial Aluminium Al–Mg–Zn–Cu(–Sc–Zr) Alloys

Role of Small Addition of Sc and Zr in Clustering and Precipitation Phenomena Induced in AA7075

“…Detailed information about electrical resistivity and microhardness HV0.5 measurements is described in References. [19,25].…”

“…The category of transformation line is changed with the content and composition of a particular element; the (non-)isothermal series of annealing steps are usually used [6,8,10,[17][18][19][20][21][22][23]. Despite having some disagreements and obscurity about the arrangement and the types of the hardening phases in the alloys, the decomposition of supersaturated solid solution is in the consistency with two precipitation sequences, where η′(MgZn2)phase (hexagonal)/η(MgZn2)-phase (hexagonal) and T′(Al2Zn3Mg3)-phase (hexagonal)/T(Al2Zn3Mg3)-phase (cubic) occur [15,19,20]. The precipitation of the semi-coherent η′-and T′-phases usually cause the age-hardening of the materials in contrast to the incoherent η-and T-phases [19,20,[22][23][24][25][26][27].…”

“…Despite having some disagreements and obscurity about the arrangement and the types of the hardening phases in the alloys, the decomposition of supersaturated solid solution is in the consistency with two precipitation sequences, where η′(MgZn2)phase (hexagonal)/η(MgZn2)-phase (hexagonal) and T′(Al2Zn3Mg3)-phase (hexagonal)/T(Al2Zn3Mg3)-phase (cubic) occur [15,19,20]. The precipitation of the semi-coherent η′-and T′-phases usually cause the age-hardening of the materials in contrast to the incoherent η-and T-phases [19,20,[22][23][24][25][26][27]. Many authors use different designations for the early precipitation phases formed during the precipitation; (co-)clusters/Guinier-Preston (GP) zones of different types usually appear during ageing at temperatures lower than ~150 °C [19,20,25,[28][29][30][31][32][33].…”

“…One possibility how to improve the potential of traditional commercial aluminum 7075-(Al-Zn-Mg-Cu-Mn-Si-Fe-) based alloys is the addition of rare earth (RE) elements (incl. Sc) and/or the addition of selected transition (TM) metals (e.g., Zr) [1,[12][13][14][15][16]19,[34][35][36][37][38][39]. The TM elements diffuse much slower than Sc and a TM-enriched shell behaves as a diffusion barrier preventing the diffusion from the Sc-rich core and this way reduces a coarsening of the core-shell secondary Al3(Sc,TM)-phase [1].…”

“…This work is based on ongoing research, which has partially been recently published in References. [15,19,20,25]. The results of positron annihilation, microhardness and resistivity measurements during the isochronal annealing and subsequent natural ageing, thermal response and corrosion behavior were suitably supplemented with the powder X-ray diffraction and microstructure observations by scanning and transmission electron and atomic force microscopy.…”