Effect of heterogeneously distributed pre-existing dispersoids on the recrystallization behavior of a cold-rolled Al-Mn-Fe-Si alloy
It is well known that strong concurrent precipitation, mainly located along grain/subgrain boundaries, results in a coarse and elongated grain structure, and unusual sharp P {011} and/or M {113} texture components during annealing of supersaturated AA3xxx-series alloys. In this study, a supersaturated as-cast Al–Mn–Fe–Si alloy was annealed at three temperature–time paths after cold rolling and their effects on the softening behavior have been analyzed and compared in terms of final grain structure and texture. In particular, material conditions with dispersoids located along grain/sub-grain boundaries were produced prior to annealing. The effects of pre-existing dispersoids as well as dispersoids formed during annealing (concurrent precipitation), both of which are heterogeneously distributed along grain/sub-grain boundaries, on the recrystallization behavior of the deformed material were investigated and compared. The results clearly show that, due to their larger sizes, these pre-existing dispersoids do not significantly increase the strength of the P/M texture components as compared to the dispersoids formed during annealing, even though the former can still affect the grain structure. It can be concluded that sharp P/M textures develop when recrystallization takes place at low temperature where nucleation of other orientations, whether from particle stimulated nucleation (PSN) or other nucleation mechanisms are suppressed by concurrent precipitation.
Evolution in microstructure and properties during non-isothermal annealing of a cold-rolled Al-Mn-Fe-Si alloy with different microchemistry states
The softening behaviour during non-isothermal annealing of a cold-rolled Al–Mn–Fe–Si model alloy was studied as a function of the state of microchemistry, in terms of the solute level of Mn, size and spatial distribution of the Mn-bearing dispersoids, as well as their temporal evolution. Microchemistry significantly affects the recrystallization microstructure, crystallographic texture as well as the mechanical property of the investigated alloy after non-isothermal annealing. The nucleation and growth of grains with different orientations are strongly dependent on both annealing temperature and microchemistry, in that pre-existing dispersoids have a less profound effect on retarding recrystallization than dispersoids forming concurrently during back-annealing. Strong concurrent precipitation suppresses nucleation and retards recrystallization, which finally leads to a coarse and pan-cake shaped grain structure, accompanied by strong P {011}〈566〉 and/or M {113}〈110〉 texture components and a relatively weaker ND-rotated cube {001}〈310〉 component. A refined grain structure with medium strength P and cube {001}〈100〉 components is obtained when the pre-existing dispersoids are coarser and fewer, and concurrent precipitation is limited. P-oriented grains are less affected by second phase particles and experience a growth advantage at low annealing temperatures (<350 °C), while M-oriented grains appear at higher temperatures. The intensity of the P texture does not necessarily increase with increasing supersaturation of Mn as observed during isothermal annealing, whereas the level of supersaturated Mn promotes the strength of the M texture. The mechanisms behind are discussed.
Further studies on fire retardant polystyrene by Friedel–Crafts chemistry
Abstract The combination of a copolymer of 4-vinylbenzyl alcohol and styrene with 2-ethylhexyldiphenylphosphate (DPP) and with metal chlorides has been studied by TGA, radiative gasification, Cone Calorimetry, and oxygen index measurements. Evidence is presented in support of a cross-linking reaction with the additives and the copolymer, which proceeds through a Friedel–Crafts mechanism. This approach reduces the peak heat release rate (HRR) by 60% as measured in the Cone Calorimeter. There is a significant reduction in the mass loss rate during the thermal degradation, and evidence of char formation is observed in the radiative gasification experiments.