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Currently, the primary commercial aluminum alloy fillers used are 4043 and 5356. However, when welded with high-strength work pieces like 6061 and 7075 aluminum alloys, the strength of weld beads significantly lags behind that of the original welded material. Both 4043 and 5356 aluminum alloys cannot be strengthened through heat treatment. The strength difference between the weld bead and base material doubles after heat treatment. In this study, an Al-Si-Cu-Mg alloy (SCM) filler modified using a heat-treatable A319 aluminum alloy was employed to investigate the post-welding microstructural and mechanical properties of specimens under room- and high-temperature conditions and after prolonged exposure in a saltwater environment (3.5 wt.% NaCl). The aim was to demonstrate that commercial aluminum alloy fillers could be substituted with a high-silicon aluminum alloy boasting excellent solidification and mechanical properties. The results revealed that, after heat treatment of the weld bead, dendrites were not eliminated, but the tensile strength increased to 310 MPa, closely matching that of commercial 6061 aluminum alloy. The strength of the weld bead remained higher than 250 MPa in high-temperature (240 °C) and saltwater environments. These findings underscore the potential application of this material. [ABSTRACT FROM AUTHOR]

In this study, trace quantities of silver, palladium, and gold were added to 5 N pure copper wires to prepare microalloyed copper (MAC) wires. The mechanical properties and electrical fatigue mechanisms of original wires and wire bonding specimens were compared to assess the differences between MAC and Au/Pd-coated copper (CPA) wires. The results indicate that the solid-solution strengthening achieved by the addition of trace alloy elements improved the microhardness and tensile properties of the wires; thus, the overall mechanical properties of the MAC wires were superior to those of a CPA wire. Moreover, after wire bonding, the MAC wires exhibited a higher first bond strength than the CPA wire. In terms of electrical properties, the addition of trace alloying elements increased resistance marginally, which resulted in MAC wires with higher dynamic resistance than the CPA wire in the early stage of electrification. At high currents, CPA wires are affected by Joule heat. The palladium atoms in the coating layer diffuse into the wire matrix, which causes the resistance to increase rapidly and thus results in a decreased fusing current. In a power cycling test, the coefficients of thermal expansion of the coating layers were different from that of the wire; thus, the CPA wire was susceptible to thermal fatigue, which led to its failure. The MAC wires had a higher power cycle life than the CPA wire. Because of their superior mechanical and electrical properties, MAC wires can replace CPA wires in the electronic packaging industry. [ABSTRACT FROM AUTHOR]

Al–Mg–Sc–Zr alloy fabricated through selective laser melting (SLM) is an additive manufacturing alloy with promising industrial potential. In this study, as-printed specimens were subjected to either single-stage or two-stage heat treatment processes to investigate the effect of temperature from room temperature to high temperature on the specimens' tensile and fatigue properties to establish a reliable reference for aerospace applications. The tensile test results indicated that the heat treatment contributed to determine the properties of the nanoprecipitate Al3(Sc, Zr) with a strengthening phase, improving tensile strength. Moreover, the dynamics strain aging (DSA) effect vanished as temperature increased. It is noteworthy that the nanoprecipitation was distributed at the boundary of the melting pool after single-stage heat treatment with the highest tensile properties in all tests. In addition, the microstructure observed after the two-stage heat treatment indicated a melting pool interface decomposition, and the nanoprecipitation was homogeneously scattered over the Al matrix, increasing strength and further delaying fatigue crack transmission. Those features build a high-fatigue-resistance foundation. TEM analysis also confirmed the promotion of Sc thermal diffusion and an Al3(Sc, Zr) precipitation transformation mechanism under two-stage heat treatment, corresponding to aforementioned inferences. The SLM Al–Mg–Sc–Zr alloy with two-stage heat treatment brings about balance between tensile properties and fatigue resistance, providing new insight into additive manufacturing with Al alloys. [ABSTRACT FROM AUTHOR]

• The microstructure evolution of heat-treated SLM Al-Ni-Cu-Fe-Zr-Sc specimens was obtained. • The phase transformation of the heat-treated specimen was investigated. • The elemental composition of the bimodal microstructure was obtained. • The nanoprecipitation in the fine-grained region was investigated to clarify the precipitation mechanism. The novel selective laser melting (SLM) Al-Ni-Cu-Fe-Zr-Sc alloy has high temperature stability, but the segregation of the melting pool boundary limits its potential applications. Because conventional heat treatment with a solid solution at 530 °C is inappropriate for the SLM Al-Ni-Cu-Fe-Zr-Sc alloy, this study used hyper-high-temperature solid-solution treatment at three temperatures (560, 570, and 580 °C for 1 h) to investigate the evolution of the melting pool structure. An artificial aging treatment was applied at 175 °C for 6 h to investigate the precipitation mechanism. The results indicated that as-printed presented a bimodal microstructure consisting of a coarse-grained (CG) region and a fine-grained (FG) region. The hyper-high-temperature solid-solution treatment promoted the decomposition of the melting pool boundary and expansion of FG region. The FG region was composed of Ni-, Cu-, and Fe-rich equiaxed grains. After aging treatment, Al 9 Fe(Cu)Ni and Al 3 (Sc, Zr) nano-scale strengthening phases could be found in the FG region. The decomposition of the melting pool boundary, bimodal microstructure, and nano-scale phases can strengthen the matrix and increase hardness. In addition, the mechanism of element diffusion in melting pool was also explored to confirm that heat treatment can reduce material deterioration caused by boundary precipitation. These characteristics mitigate the disadvantages of the SLM Al-Ni-Cu-Fe-Zr-Sc alloy in terms of its strength directionality and establish its potential for use in aerospace applications. [ABSTRACT FROM AUTHOR]

Metal powder metallurgy (PM) is widely utilized in the tool and automotive industries due to its near-net forming advantages. While PM aluminum alloys have been explored in numerous studies, their practical engineering applications are still limited. Thus, this research delves into the nuanced aspects of PM Al-Si-Mg-Fe alloy. By employing hot-rolled dynamic recrystallization to control the metallurgical texture and introducing T6 treatment to refine the microstructure. These optimizations aim to enhance the properties of PM aluminum alloy materials. Results revealed that grain coarsening in the PM Al-Si-Mg-Fe alloy hampers the grain boundary strengthening effects, thus limiting the strength. Moreover, the solid-solution treatment applied to the PM specimens efficiently disperses silicon particles within the matrix, preventing the aggregation of silicon particles and the associated brittle effect caused by interface peeling. By implementing a three-stage process, sintering-rolling-T6 treatment, the rolled-T6 exhibited impressive tensile strength (291 MPa) and ductility (17 %), highlighting the excellent engineering applicability of PM Al-alloys. TEM analysis confirmed the presence of nanoprecipitation Al 3 Mg and Al 9 Fe 2 hard components within the matrix, contributing to the strength enhancement. These findings not only represent a significant milestone in the advancement but also provide valuable references for engineering applications in the field of PM Al-alloys. • PM technology enhances Al-Si-Mg-Fe alloy applications. • Three-stage process optimizes microstructure and properties. • Microstructural effects and phase distribution are compared. • Reveals Al 9 Fe 2 and Al(Si) 3 Mg strengthening mechanisms. [ABSTRACT FROM AUTHOR]

The melt refining process of Martensitic stainless steel smelting is closely related to the characteristics of the matrix; the formation mechanism and distribution of carbides, especially, influence the mechanical properties of steel. In this study, three different melt refining processes of 440 stainless steel were used for analysis: aluminum reduction process (440 M-Al), silicon reduction process (440 M-Si), and electro slag remelting (440 C-ESR). The results show the main carbides of 440 stainless steel after three different melt refining processes are M7C3 and M23C6. The carbides of 440 M-Al and 440 M-Si are fine particles; the carbide of 440 C-ESR is a small block. The 440 M-Al carbides are micron- and nanoscale-sized particles. The micron-sized carbides solidify and aggregate at the unit cell boundary, and the structure is Cr7C3. There are gaps between the carbide particles, and the solid solution carbon content of the adjacent matrix is high, which makes the hardness of the matrix greater than that of the carbide aggregation area. On the contrary, the matrix of 440 C-ESR solid dissolves many alloying elements, and the fine lump carbide is also Cr7C3. The carbide diffusion interface layer of 440 C-ESR can improve the bonding characteristics of the interface of the carbide and the matrix, thus enhancing the mechanical properties.

Currently, the primary commercial aluminum alloy fillers used are 4043 and 5356. However, when welded with high-strength work pieces like 6061 and 7075 aluminum alloys, the strength of weld beads significantly lags behind that of the original welded material. Both 4043 and 5356 aluminum alloys cannot be strengthened through heat treatment. The strength difference between the weld bead and base material doubles after heat treatment. In this study, an Al-Si-Cu-Mg alloy (SCM) filler modified using a heat-treatable A319 aluminum alloy was employed to investigate the post-welding microstructural and mechanical properties of specimens under room- and high-temperature conditions and after prolonged exposure in a saltwater environment (3.5 wt.% NaCl). The aim was to demonstrate that commercial aluminum alloy fillers could be substituted with a high-silicon aluminum alloy boasting excellent solidification and mechanical properties. The results revealed that, after heat treatment of the weld bead, dendrites were not eliminated, but the tensile strength increased to 310 MPa, closely matching that of commercial 6061 aluminum alloy. The strength of the weld bead remained higher than 250 MPa in high-temperature (240 °C) and saltwater environments. These findings underscore the potential application of this material.