Microstructures and properties of wire-arc additively manufactured ultra-high strength aluminum alloy under different heat treatments

The microstructures, mechanical properties and corrosion behaviors of the ultra-high strength Al–Zn–Mg–Cu-Sc aluminum alloy fabricated by wire-arc additive manufacturing process using a self-prepared 7B55-Sc filler wire were systematically investigated under different heat treatments. The results showed that the microstructures of the as-deposited, T6, T73, and retrogression and re-aging (RRA) heat treatments were all composed of fine equiaxed grains with a size of about 6.0 μm. The grain boundary precipitates (GBPs) of the as-deposited sample were very coarse and continuously distributed along the grain boundaries, and the intragranular precipitates (IGPs) mainly consisted of a small amount of ηMg(Zn,Cu,Al)2 and η′ phases. After T6 heat treatment, the GBPs became much finer, but still continuously distributed along the grain boundaries. The IGPs mainly consisted of fine GP zones and η′ phases. After RRA heat treatment, the GBPs became coarser and discontinuously distributed along the grain boundaries. The IGPs were composed of η′ phases and ηMg(Zn,Cu,Al)2 phases. After T73 heat treatment, the GBPs became much coarser and sparsely distributed along the grain boundaries. The IGPs mainly consisted of coarser ηMg(Zn,Cu,Al)2 phases. The T6 heat-treated sample achieved the highest tensile strength of 618 MPa. While the strength of T73 heat-treated sample was sacrificed by up to 17% compared with the T6 heat-treated sample, but the corrosion resistance was the best of all heat-treated conditions. After RRA heat treatment, the strength was about 10% lower than the strength of the T6 condition, but the corrosion resistance was better than that of the T6 heat-treated sample

Enhancing strength, ductility, and fatigue performance of Al-Zn-Mg-Cu-Sc-Zr alloy using a hybrid approach: Wire-arc directed energy deposition and interlayer friction stir processing

Porosity defects are the main issues faced by aluminum alloys manufactured by wire-arc directed energy deposition (WA-DED), which seriously affect the mechanical properties of WA-DED aluminum alloys, especially the fatigue properties. Thus far, there is still no effective solution for the elimination of porosity in high-strength WA-DED aluminium alloys. In this study, an innovative hybrid WA-DED + interlayer friction stir processing (FSP) method was applied to successfully fabricate thick-walled Al-Zn-Mg-Cu-Sc-Zr aluminum alloy component with enhanced strength-ductility and fatigue properties by utilizing a custom 7B55-Sc wire. The porosity defects caused by the WA-DED process were significantly reduced in the FSP effective zone, and the original continuous grain boundary eutectic structures were broken up and dispersed along the grain boundaries. The grains were also further refined with an average size of about 1.1 ± 0.2 μm in the stirring zone (SZ) and 1.6 ± 0.3 μm in the overlapping SZ. The nanoscale intragranular precipitates (IGPs) were mostly composed of both rod-like ηMg(Zn,Cu,Al)2 phases and secondary Al3(Sc, Zr) phases. The yield strength (YS), ultimate tensile strength (UTS) and uniform elongation (EL) in the horizontal and vertical directions were all substantially improved comparing with the WA-DED 7B55-Sc component, especially in the horizontal direction, reaching 387 ± 7 MPa, 511 ± 15 MPa and 14.6 ± 0.5%, respectively. The fatigue property after 1 × 107 cycles for the WA-DED + interlayer FSP 7B55-Sc sample was significantly increased by 81%, reaching 170 MPa in vertical direction compared to 100 MPa of the WA-DED 7B55-Sc component

Microstructural Evaluation and Tensile Properties of Al-Mg-Sc-Zr Alloys Prepared by LPBF

Laser powder bed fusion (LPBF) is a typical additive manufacturing technology that offers significant advantages in the production of complex components. With the rapid heating and cooling characteristics of LPBF, a large amount of solid solution of alloying elements in the matrix can be achieved to form supersaturated solid solutions, thus enhancing the properties of LPBF alloys. For the unique microstructure, the heat treatment process needs to be adjusted accordingly. In this work, a Zr/Sc-modified Al-Mg alloy processed by laser powder bed fusion (LPBF) with relatively low cost and good mechanical properties was investigated. The fine microstructure was obtained under rapid solidification conditions. The nanoscale Al3(Sc,Zr) particles precipitated at the molten pool boundary during solidification. These particles, as effective heterogeneous nucleators, further refined the α-Al grains and improved the mechanical properties of the alloy. As a result, the alloy exhibited a heterogeneous microstructure consisting of columnar grains in the center of the molten pool and equiaxed grains at the boundaries. The rapid solidification resulted in the supersaturation of solute atoms in the α-Al matrix, which significantly enhanced the solid solution strengthening effect. With the LPBF processing parameters of a combination of a laser power of 250 W, a laser scanning speed of 833 mm/s, and stripe scanning mode, the tensile strength of the alloy reached 401.4 ± 5.7 MPa, which was significantly higher than that of the cast alloys with aging treatment (281.1 ± 1.3 MPa). The heat treatment promoted the formation of secondary Al3(Sc,Zr), Mn/Mg-rich phases. The ultimate tensile strength and elongation at fracture after aging at 325 °C for 2 h were 536.0 ± 1.7 MPa and 14.8 ± 0.8%, respectively. The results provide insight into the preparation of aluminum alloys with relatively low cost and excellent mechanical properties

Effect of grain refinement and crystallographic texture produced by friction stir processing on the biodegradation behavior of a Mg-Nd-Zn alloy

The application of a single pass of friction stir processing (FSP) to Mg-Nd-Zn alloy resulted in grain refinement, texture evolution and redistribution of second phases, which improved corrosion resistance. In this work, an as-rolled Mg-Nd-Zn alloy was subjected to FSP. The microstructure in the processed zone of the FS-400 rpm alloy exhibited refined grains, a more homogenous grain size distribution, less second phases, and stronger basal plane texture. The corrosion behavior assessed using immersion tests and electrochemical tests in Hank's solution indicated that the FS-400 rpm alloy had a lower corrosion rate, which was attributed to the increase of basal plane intensity and grain refinement. The hardness was lowered slightly and the elongation was increased, which might be attributed to the redistribution of the crushed second phases