Evaluation of the Microstructure and Mechanical Properties of a New Modified Cast and Laser-Melted AA7075 Alloy

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy.

Influence of Zn and Sn on the Precipitation Behavior of New Al–Mg–Si Alloys

In this study, we demonstrate how Zn and Sn influence hardening behavior and cluster formation during pre-aging and paint bake treatment in Al–Mg–Si alloys via hardness tests, tensile tests, and atom probe tomography. Compared to the standard alloy, the Sn-modified variant shows reduced cluster size and yield strength in the pre-aged condition. During the paint bake cycle, the clusters start to grow very fast and the alloy exhibits the highest strength increment. This behavior is attributed to the high vacancy binding energy of Sn. Adding Zn increases the formation kinetics and the size of Mg–Si co-clusters, generating higher yield strength values for both the pre-aged and paint baked conditions. Simultaneous addition of Zn and Sn creates a synergistic effect and produces an alloy that exhibits moderate strength (and good formability) in the pre-aged condition and accelerated hardening behavior during the paint bake cycle.

Thermal Stability of Intermetallic Cu–Sn Interconnections for High Temperature Applications

New technology based on mixing of standard alloy SnCu in form of solder paste with copper paste was presented. This technology allows the production of solder joints with higher standoff consisting of intermetallic compounds. Such solder joints were qualified for high temperature applications by investigation of thermal stability of overlapped solder joints. For this purpose a special test bench for the investigation of remelting temperature up to 300°C was developed.

Intermetallic connections for high temperature applications

New technology based on mixing of standard alloy SnCu in form of solder paste with copper paste was presented. This technology allows the production of solder joints with higher stand-off consisting of intermetallic compounds. Such solder joints were qualified for the high temperature applications by investigation of thermal stability of overlapped solder joints. For this purpose a special test bench for the investigation of remelting temperature up to 300 °C was developed.

Nucleation and Growth of Primary Silicon Crystals in AlSi Alloy after Modification with CuP and Overheating to a Temperature of 920°C

The article describes the process of crystallization of an AlSi17Cu5 (the A3XX.X series according to ASTM standard) alloy which has been modified with 0.05 wt. % P (CuP10 master alloy) and overheated to a temperature of 920°C. It has been shown that, so-called, "time-temperature treatment" (TTT) of alloy in the liquid state, which consists in overheating the alloy to a temperature above Tliq (about 250-300°C), holding at this temperature and rapid cooling, alters the morphology of primary silicon crystals. By the ATD method of thermal analysis, the characteristic temperature of crystallization (Tliq., TEmin., TEmax., TE(Cu), TE(Fe), Tsol.) were determined, and exothermic effects of the modifier and high-degree overheating on the crystallization course of the investigated alloy were examined. A new mechanism of proeutectic crystallization of the a(Al, Me=Cu, Fe) dendrites was proposed. The course of this process is dynamic enough to promote, due to local undercooling, the evolution of heat, which in the ATD curve appears as a well visible additional exothermic effect designated as TX. It is due to the presence in the liquid alloy of microregions with varied content of dissolved silicon.

A Method for Predicting the Chemical Composition of Recycled Aluminum Alloys

The present paper describes a method for predicting the imminence (hereafter referred as ‘quality’) of the chemical composition of a recycled alloy to that of a standard alloy of aluminum recycled alloy made from aluminum scrap (used automotive components). The present method allows the chemical composition of a recycled alloy to be predicted. The method has been validated experimentally, and the results obtained showed that the composition of the recycled alloy was close to that of the predicted one. These findings indicate that the present method can be successfully used for any other recycled alloys to predict the alloy composition based on the in-coming scrap alloys. In this work, the chemical composition of a synthesized recycled alloy was compared to an ASTM standard alloy with the nearest composition. It was found that the two compositions were very comparable. A deviation factor has been defined in order to understand the quality of the recycled alloy obtained with reference to the ASTM alloy.

Research of Color and Discoloration Resistance of 18K Rosy Gold for Ornaments

75Au25Cu was the basic rosy gold alloy for jewelry, but it had no good brightness and was prone to tarnish and darken. This paper modified this basic alloy through multiple elements and less (micro) alloying, and measured its color and discoloration-resistance. The results showed that small amounts of zinc plus trace of silicon and cerium helped to improve the color and discoloration-resistance of the alloy, the initial colorimetric values fell in between 5N-18 standard alloy and 75Au25Cu basic alloy, while the brightness reached nearly 86, implying that the color was superior to the requirements of EN28654:1993 and ISO8654:1997. Moreover, the test alloy had better preferable resistance to darkening, discoloration and oxidation. All these performances indicated that the test alloy could meet the color requirement of rosy gold for ornaments such as clocks & watches and jewelries.