Rio Tinto (Canada)

This study examines the effects of Sc and Zr microalloying on the strength, electrical conductivity (EC), and thermal stability of Al-Mg-Si-Cu alloys developed for high-temperature conductor applications. Two alloy compositions were investigated: Alloy A (Al-Mg-Si-Cu base alloy free of Sc or Zr) and Alloy B (with 0.07 wt% Sc and 0.086 wt% Zr). Both alloys were subjected to a tailored thermomechanical treatment involving pre-aging at 120 °C, post-aging at 140 °C and 160 °C, and over-aging at 300 °C for 5 h. Alloy B was further processed using solution treatments at 500 °C (BS500) and 530 °C (BS530). The BS530 condition, post-aged at 160 °C, achieved the highest tensile strength of 518 MPa but exhibited relatively low electrical conductivity (45.0 %IACS). The BS500, over-aged at 300 °C, exhibited the best overall thermal stability due to forming finer and thermally stable Al 3 (Sc,Zr) dispersoids, and reached the highest EC (54.1 %IACS) with reasonably high strength (290 MPa). This strength value greatly surpasses the IEC 62004 AT2 requirement of 225 MPa, although conductivity fell slightly below the target of 55 % IACS. In contrast, the base alloy (A) achieved a maximum EC of 55.1 %IACS but significantly lower strength and thermal-resistant performance. Overall, the Sc and Zr microalloying, combined with tailored thermomechanical processing, enabled balanced combinations of strength, EC, and long-term thermal resistance—supporting the design and processing of next-generation aluminum conductors for elevated-temperature applications.

The present study investigated the microstructure, processability, and mechanical strength of an AlSi9Mg-20vol.%SiC composite to assess its processing and mechanical performance during the laser powder bed fusion process. A simple laser surface remelting approach was adopted to simulate laser-based rapid solidification. The results revealed that this composite generally exhibited good laser processability, and the samples with the highest laser energy density and lowest scan speed possessed the best processability owing to the elimination of microcracks and pores. After laser processing, all the samples displayed a fine Al-Si cellular structure accompanied by in-situ formed fine needle-shaped Al4SiC4 particles. Increasing laser energy density considerably increased the area fraction of the Al4SiC4. The T5 aging treatment preserved the fine cellular structure and promoted the precipitation of a large number of Si nanoparticles and MgSi precipitates. During T6 solid solution treatment, the Si networks were broken down into coarse Si particles, disintegrating the cellular structure and reducing the strength. The T5 treatment was identified as the most suitable post-heat treatment for enhancing the microhardness and strength of the composite. Compared to conventionally laser-processed AlSi10Mg alloys, the AlSi9Mg-20vol.%SiC composite exhibited a significant increase in microhardness and yield strength.

ABSTRACT Near-infrared spectra from the IRTF/SpeX and Blanco/ARCoIRIS telescope/instrument combinations are used for spectroscopic classification, to measure radial velocities, and for the inference of astrophysical properties of 51 Gaia-selected nearby ultracool dwarfs. In this sample, 44 are newly classified in the near infrared. All but one of the UCDs are within 100 pc, and 37 lie within 50 pc. We find a total of 26 M-types, 24 L-types, and one T-type in our sample. The positions of the majority of the UCDs on colour–magnitude diagrams and with evolutionary cooling track plots indicate that they are largely old and stellar in nature. There are a few UCDs of particular interest which lie away from expected trends, highlighting potential young, binary, and thick disc/subdwarf UCDs. From spectral and kinematic analyses, we identify UCDs of particular interest for further investigation, including seven potentially young UCDs, three thick disc UCDs, one subdwarf, six wide binaries, and six unresolved binaries.