Effect of Rotation Speed on Microstructure and Mechanical Properties of Continuous Drive Friction Welded Dissimilar Joints of 6061-T6 Al and Copper

The continuous drive friction welding of 6061-T6 Al and copper was investigated herein. The results show that with an increase in rotation speed, the width of the welded zone was gradually increased with the generation of higher temperatures, and the grain size in the dynamic recrystallization zone on the Al side first decreased and then increased due to the combined effect of heat and force. The microhardness on the bonding surface was significantly greater than that of the base materials due to the presence of intermetallic compounds, and there was a softening zone on both sides of the bonding surface, which was progressively more significant with an increase in the rotation speed. The ultimate tensile strength (UTS) of the welded joints first increased and then decreased with an increase in rotation speed. When the rotation speed was 1000 rpm, the UTS was at its peak value of 212 MPa, which reached 73.1% of the strength of the 6061-T6 Al base material

Microstructure and Properties of Aluminum–Graphene–SiC Matrix Composites after Friction Stir Processing

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture

Improved Compressive Properties of Lattice Structure Based on an Implicit Surface Hybrid Optimization Design Method via Selective Laser Melting

In recent years, the lattice structure produced by additive manufacturing is a type of metal foam that has been increasingly investigated for its unique mechanical properties. However, the conventional Computer-Aided Design (CAD) is inefficient, the triply periodic minimal surfaces are rarely mixed, and the smooth transitions at the boundaries are not considered. In this study, a hybrid optimization design method based on implicit surfaces is proposed, which combines multiple implicit surfaces to achieve the continuous change in the curvature at the structure junctions and reduce the stress concentration. The hybrid lattice structures designed by this method were additively manufactured using 316L alloy via a selective laser melting. The results of the finite element analysis and mechanical compression test show that the hybrid lattice structures generated by this method exhibit a higher yield strength and energy absorption. These works can be used for other implicit surfaces, improve and enrich the types of implicit surfaces, and provide more good choices for practical applications

Weighted Information Models for the Quantitative Prediction and Evaluation of the Geothermal Anomaly Area in the Plateau: A Case Study of the Sichuan–Tibet Railway

The prediction of geothermal high-temperature anomalies along the plateau railway will be helpful in the construction of the project and its later management. Taking the Sichuan–Tibet railway as the study area and based on Landsat8 thermal infrared images, map data, and measured data regarding the cause and distribution of geothermal high-temperature anomalies, through correlation analysis, we selected six impact factors including the LST, combined entropy of geological formation, fault density, buffer distance to rivers, magnetic anomaly, and earthquake peak acceleration as the input maps of the model. The index-overlay information model, the weights of the entropy information model, and the weights of the evidence information model were established to quantitatively predict the geothermal anomaly in the study area, and the prediction maps were divided into four classes. The results show that the weights of the evidence information model achieved a high prediction accuracy; the success index and the ratio of the high anomaly area reached 0.0053% and 0.872, respectively, and the spatial distribution of the geothermal points is basically consistent with the prediction results. This research can act as a reference for the design and construction of the Sichuan–Tibet railway

MOF influences meiotic expansion of H2AX phosphorylation and spermatogenesis in mice.

Three waves of H2AX phosphorylation (γH2AX) have been observed in male meiotic prophase I: the first is ATM-dependent and occurs at leptonema, while the second and third are ATR-dependent, occuring at zygonema and pachynema, respectively. The third wave of H2AX phosphorylation marks and silences unsynapsed chromosomes. Little is known about H2AX phosphorylation expands to chromatin-wide regions in spermatocytes. Here, we report that histone acetyltransferase (HAT) MOF is involved in all three waves of H2AX phosphorylation expansion. Germ cell-specific deletion of Mof in spermatocytes by Stra8-Cre (Mof cKO) caused global loss of H4K16ac. In leptotene and zygotene spermatocytes of cKO mice, the γH2AX signals were observed only along the chromosomal axes, and chromatin-wide H2AX phosphorylation was lost. In almost 40% of early-mid pachytene spermatocytes from Mof cKO mice, γH2AX and MDC1 were detected along the unsynapsed axes of the sex chromosomes, but failed to expand, which consequently caused meiotic sex chromosome inactivation (MSCI) failure. Furthermore, though RAD51 was proficiently recruited to double-strand break (DSB) sites, defects in DSB repair and crossover formation were observed in Mof cKO spermatocytes, indicating that MOF facilitates meiotic DSB repair after RAD51 recruitment. We propose that MOF regulates male meiosis and is involved in the expansion of all three waves of H2AX phosphorylation from the leptotene to pachytene stages, initiated by ATM and ATR, respectively

RAD51 foci persist in <i>Mof</i> deleted pachytene and diplotene spermatocytes.

<p>Immunofluorescence staining for SYCP3 (red), RAD51 (green) and H1T (blue) in control and <i>Mof</i> cKO spermatocytes at early pachynema (A), late pachynema (C) and diplonema (E). Scale bars, 10 μm. The mean number of RAD51 foci per cell in control and <i>Mof</i> cKO early pachytene (B), mid-late pachytene (D) and diplotene spermatocytes (F). Data are presented as mean ± SD. n, the number of analyzed spermatocytes from 3 mice. ** <i>P</i><0.01, Mann-Whitney test.</p

MSCI is disturbed in <i>Mof</i> cKO mice.

<p>A. Immunofluorescence with SYCP3 (red) and H3K4me3 (green) antibodies in control and <i>Mof</i> cKO spermatocytes. Arrows indicate the sex chromosomes. Scale bars, 10 μm. B. The ratio of early-mid pachytene cells with negative (normal) or positive (abnormal) H3K4me3 staining around sex chromosomes from control and <i>Mof</i> cKO mice. n, the number of analyzed spermatocytes from 3 mice. C. Immunofluorescence with SYCP3 (red) and ATRX (green) antibodies in control and <i>Mof</i> cKO spermatocytes. Scale bars, 10 μm. D. The ratio of early-mid pachytene cells with (abnormal) or without (abnormal) ATRX staining from control and <i>Mof</i> cKO mice. n, the number of analyzed spermatocytes from 3 mice. E. Relative levels of X- or Y-linked genes in control and <i>Mof</i> cKO pachytene spermatocytes. The gene levels (normalized to <i>Actb</i> expressed in the same sample, with values in control spermatocytes designated as 1), were determined by Real-time PCR to assess MSCI. <i>Dazl</i> and <i>Setx</i> are located on autosomes. <i>Atrx</i>, <i>Usp26</i> and <i>Tktl1</i> are X-linked, and <i>Rbmy</i> and <i>Ube1y</i> are Y-linked genes. Data are expressed as mean ± SD from three independent experiments. * <i>P</i><0.05, ** <i>P</i><0.01, Student’s <i>t</i>-test.</p

<i>Mof</i> deletion disturbs all three waves of chromatin-wide expansion of H2AX phosphorylation during meiosis.

<p>Immunofluorescence staining for SYCP3 (red) and γH2AX (green) in control and <i>Mof</i> cKO spermatocytes. (A) Leptonema, (B) Zygonema, (C) Pachynema and (D) Diplonema. Scale bars, 10 μm.</p