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The effects of Sc, Mg and Si elements in an Al-Cu alloy have been studied by means of hardness tests and transmission electron microscopy analysis. The experimental results show that additions of Sc, Mg and Si can improve the heat resistance of the Al-Cu alloy. The Sc/Mg/Si segregation-sandwiched structure is the most stable, when compared with Sc segregation or Si/Sc co-segregation at the interface of θ′/Al. The additions of Si and Mg promote the aging–hardening response of the Al-Cu alloy. Mg is a micro-alloying element with great potential in stabilizing the size of θ′ phases, which further promotes the number density greatly. Consequently, the Al-Cu alloy achieves a high strength, matched with excellent thermal stability, due to the microalloying of Sc/Mg/Si solutes. [ABSTRACT FROM AUTHOR]

The Al–Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100–550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical—both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates. [ABSTRACT FROM AUTHOR]

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and strengthening mechanism. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are employed to examine the changes in the microstructure resulting from various solid solution treatments and aging treatments. The best strengthening effect can be achieved when the solubility of the MgSi phase and precipitate β″ (Mg2Si phase) is at their maximum. The addition of Er and Zr elements promotes the precipitation of the β″ phase and makes the b″ phase more finely dispersed. The aging strengthening of alloys is a comprehensive effect of the dislocation cutting mechanism and bypass mechanism, the joint effect of diffusion strengthening of Al3(Er,Zr) particles and the addition of Er and Zr elements promoting the precipitation strengthening of β″ phases. In this paper, by adding Er and Zr elements and exploring the optimal heat treatment system, the yield strength of the alloy reaches 437 MPa and the tensile strength reaches 453 MPa after solid solution treatment at 565 °C/30 min and aging at 175 °C/10 h. [ABSTRACT FROM AUTHOR]

The precipitation and intergranular corrosion (IGC) behavior of Al–1.0Mg–0.6Si–Cu (wt.%) alloys with the addition of Cu ranged from 0.3 to 0.6 wt.% were investigated by optical microscope and transmission electron microscopy. The results indicated that the Cu addition significantly improves the hardness of the alloys during under-aging progress by accelerating the precipitation of GP zones. The addition of Cu has changed the composition of precipitation and facilitated the formation of β′′-Mg5Si6 precipitates with high density and fine distribution. When the Cu content is added to 0.6 wt.%, the type of precipitation has changed. In addition to the needle-shaped β′′ phase, a new-plate Q′ phase precipitated during peak-aging conditions. The 0.6 wt.% Cu alloy shows superior strength with tensile yield strength of 328 MPa, ultimate tensile strength of 368 MPa, and elongation of 16.0%. However, the IGC resistance decreased with the Cu content increasing from 0.3 to 0.6 wt.%, which mainly resulted from the segregation of Cu elements and the formation of continuous Q′ precipitates at the grain boundaries. [ABSTRACT FROM AUTHOR]

The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, MgZn intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers. [ABSTRACT FROM AUTHOR]

An abnormal reverse transition of intergranular corrosion from sensitization to stabilization was observed in the Al-6.4 Mg-0.43Mn-0.37Er-0.17Zr alloy at low annealing temperatures between 220 and 260 °C for the first time. The reverse stabilized alloy annealed at 240 °C for 5 h had excellent long-term corrosion resistance in the deformed state. The corresponding transmission electron microscopy analysis showed that Al 3 Mg 2 precipitates distributed separately along grain boundary, at triple junctions and the Al 6 Mn phase boundary. The combination of the low temperature reverse stabilization and retarded recrystallization by addition of Er and Zr caused the high Mg aluminum alloy to exhibit high corrosion resistance and strain hardening. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The recrystallization behavior of Al-6Mg-0.4Mn-0.15Zr-xSc (x = 0.04, 0.07, 0.10 wt%) alloys was studied using micro-hardness test, optical microscopy and transmission electron microscopy (TEM). The optical micrographs of the alloys with different Sc contents after being annealed at 100–550 °C for 1 h showed that the recrystallized nucleus formed between 275 and 325 °C at the original grain boundaries, and grew quite slowly until 550 °C and above, indicating a 250 °C large span of recrystallization starting and finishing temperatures in the alloys. The TEM observation showed the stripe distributed spherical Al 3 (Sc,Zr) particles with phase rich region and phase poor region. The recrystallized subgrains with partial HAGBs was found at the phase poor region, but was pinned at the boundary of the phase rich region. The recrystallization driving and pinning pressures of the phase rich regions of the alloys with 0.04 and 0.1Sc wt% were estimated according to Zener drag mode. The results indicated an effective pinning effect of Al 3 (Sc,Zr) particles on the recrystallized grain at lower than 475 °C. The large span between recrystallization starting and finishing temperatures could be attributed to the stripe distribution of the Al 3 (Sc,Zr) particles. Graphical Abstract Unlabelled Image Highlights • Recrystallization starting temperature increases 25–75 °C by addition of Sc and Zr. • Recrystallization finishing temperature increases ≥250 °C by addition of Sc and Zr. • A large span between recrystallization starting and finishing temperatures • Spherical Al 3 (Sc,Zr) particles exhibit the stripe distribution. • Recrystallized grain nucleate at phase poor region, but was pinned at rich region [ABSTRACT FROM AUTHOR]

• Influence of Zn/Mg ratio on the microstructure and mechanical properties of Al-Zn-Mg alloys. • The hardness of the alloy with the Zn/Mg ratio of 2.38 aged was highest. • Spherical T′ phases was dominant in the three alloys. • Precipitates of alloys with Zn/Mg ratio of 1.61 and 3.93 significantly coarsened. The influence of Zn/Mg ratio on microstructure and mechanical properties of Al-Zn-Mg alloys with the same Zn + Mg contents has been investigated through microhardness test, electrical conductivity test and transmission electron microscopy (TEM). In this study, Zn/Mg ratio was changed from 1.61 to 3.93 with Zn + Mg content of 6 wt%. The results showed that the Vickers hardness of the alloy with the Zn/Mg ratio of 2.38 aged at 120 ℃ for 48 h was highest. Through TEM observation, strengthening precipitates in investigated alloys were mainly spherical T′ phases and a few plate-like η′ phases. With the increase of Zn/Mg ratio, T′ phase fraction in alloys decreased from 88% to 81%, and the corresponding η′ phase fraction increased from 12% to 19%. As aging at 120 ℃ from 48 h to 168 h, the coarsening degree of precipitates of alloy A and alloy C were both greater than that of alloy B. When the Zn + Mg content was 6 wt%, the alloy with the Zn/Mg ratio of 2.38 had optimum microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]

The intergranular corrosion and β phase evolution of 5083 aluminum alloy containing Er and Zr during annealing at 100–230 °C were studied using mass loss tests and transmission electron microscopy. The mass loss curves showed that when annealing temperature changed from 200 to 220 °C, the alloy was subjected to a transition from sensitized state to stabilized state, corresponding to the change of nucleation position of β precipitates from grain boundaries to triple junctions. Particularly, when the annealing temperature was at 210 °C, this transition could also happen when the annealing time was increased from 0.5-10 h to 15-24 h, associated with the change in the shape of β precipitates. The classical nucleation analysis with the consideration of Mg segregation showed the nucleation rates at grain boundary and triple junction were 1013 and 1011 m−3 s−1 at sensitization temperature 150 °C, but 109 and 1010 m−3 s−1 at stabilization temperature 220 °C, suggesting the change of nucleation site with increasing temperature. The analysis of diffusion flux of Mg around β precipitate suggested that the shape change of β precipitates from elongate to spheroidal at 210 °C was attributed to the dominant interface diffusion over the grain boundary diffusion with the increase of time. Unlabelled Image • The intergranular corrosion and microstructure in 5083 alloy with Er and Zr upon annealing were systematically studied. • The transition of sensitized to stabilized state was attributed to different nucleation locations of β phase at 200-220°C. • The sensitization and reversal process at 210°C was attributed to elongation and spheroidization of grain boundary β phase. • The nucleation rate and the morphology evolution of β phase along grain boundary were intensively discussed. [ABSTRACT FROM AUTHOR]