An additively manufactured Al-14.1Mg-0.47Si-0.31Sc-0.17Zr alloy with high specific strength,good thermal stability and excellent corrosion resistance

A novel Al-14.1 Mg-0.47 Si-0.31 Sc-0.17 Zr alloy was applied in the printing process of selective laser melting(SLM),and the corresponding microstructural feature,phase identification,tensile properties and corrosion behavior of the Al Mg Si Sc Zr alloy were studied in detail.As fabricated at 160 W and 200 mm/s,the Mg content of bulk sample decreased to 11.7 wt%due to the element vaporization at high energy density,and the density of this additively manufactured Al Mg Si Sc Zr alloy was 2.538 g/cm^(3),which is4.2%8.5%lighter than that of other SLM-processed Al alloys.After heat-treated(HT)at 325℃and 6 h,the microstructure was almost unchanged with an alternate distribution of fine equiaxed crystals and coarse columnar crystals.Nano-sized Al3(Sc,Zr)and Mg_(2)Si phases precipitated dispersedly in the Al matrix,and the tensile strength increased from 487.6 MPa to 578.4 MPa for precipitation strengthening and fine grain strengthening.With a fine grain size of 2.53μm,an excellent corrosion resistance was obtained for the as-printed(AP)Al Mg Si Sc Zr alloy.While the corrosion resistance of HT sample decreased slightly for the formation of non-dense oxide layer and pitting corrosion induced by diffuse precipitation distribution.This SLM-printed Al Mg Si Sc Zr alloy with high specific strength,good thermal stability and excellent corrosion resistance has broad prospects for the aerospace and automotive applications.

New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength

Bulk laminate structure of Ti-alloy/Ti-based metallic glass composite （MGC） was prepared by melting a preform of alternate stack-up foils in the high vacuum atmosphere. The composite demonstrates a good combination of yield strength （-1618MPa）, plasticity （-4.3%） and specific fracture strength （384 × 10^3 N m kg^-1 ） in compression. The maintained yield strength results from the unique microstruc- ture composed of the Ti layer, the solution layer with gradient structure and the MGC layer. Such a multilayer structure effectively inhibits the propagation of shear band, leading to the enhanced plastic- ity. Those extraordinary properities suggest that combining ductile lamella with brittle metallic glass （MG） by such a lay-up method can be an effective way to improve mechanical properties of MG.

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete(MCAC)on Non-Destructive Testing

Basic magnesium sulfate cement coral aggregate concrete(MCAC)is a new type of concrete consisting of basic magnesium sulfate cement,coarse coral aggregate,coral reef sand and seawater.The rebound hammer(RH),the ultrasonic pulse velocity(UPV)and the compressive strength(fcu)tests of 14 sets of cube specimens of the MCAC after 28 d of aging were conducted.The impact of the content and length of sisal fiber on the relationship between the fcu-RH and the fcu-UPV was determined.A mathematical model was established to predict the strength of the MCAC using the UPV,RH,and comprehensive UPV/RH methods and to obtain the curves of test strength.The applicability of the test strength curves of ordinary portland concrete(OPC),light-weight aggregate concrete(LAC),and coral aggregate concrete(CAC)to MCAC was assessed.The results showed that the test strength curves of OPC,LAC and CAC were inappropriate to determine the strength of MCAC using non-destructive method.The relative standard error of the curves of test strength of the RH method and the comprehensive method met the specifications,whereas that of the UPV method did not.

Design and fabrication of lightweight AlCrFeNiTi_(x) compositionally complex alloys with exceptional specific strength

This study focuses on compositionally complex alloys(CCAs),aiming to achieve a balance between high strength and low density for new energy and aerospace applications.The composition of AlCrFeNiTi_(x) CCAs is strategically guided by employing density functional theory and the theoretical design of thermodynamic calculations.Bulk CCAs,particularly AlCrFeNiTi_(0.25) alloy,demonstrate remarkable specific yield strength(1640.8 MPa) and 22.7% maximum strain.The incorporation of Ti facilitates the formation of lightweight and high-strength L2_(1)phase,contributing to the overall high specific strength.Synergistic effects of grain boundary strengthening,solid solution strengthening,Orowan strengthening and Peierls flow stress further enhance strength.Detailed exploration of micros tructural changes during fracture reveals the role of ordered phases in suppressing crack propagation and absorbing energy within disordered phases,thereby improving the toughness and fracture resistance of CCAs.These methods and discoveries establish a robust foundation for advancing the development of novel lightweight CCAs.

Effects of Nitrogen on the Glass Formation and Mechanical Properties of a Ti-Based Metallic Glass

Effects of nitrogen addition on glass formation and mechanical properties of the Ti42.5Cu40Zr10Ni5Sn2.5 metallic glass were systematically investigated. It was found that a small amount of nitrogen addition facilitated the glass formation by suppressing formation of the competing eutectic structure. Unlike large atomic size elements such as Hf and Pd which usually deteriorate specific strength, nitrogen can also increase the specific strength of the current Ti-based BMGs. The results are not only helpful for understanding glass-forming ability in general, but also useful in developing cost-effective, high-performance Ti-based bulk metallic glasses with enhanced glass-forming ability.

Mechanical Response of Triply Periodic Minimal Surface Structures Manufactured by Selective Laser Melting with Composite Materials

It is of significance but remains a pivotal challenge to simultaneously enhance the strength and lightweight levels of porous structures.We provide an innovative strategy to improve the strength of porous structures with unchanged lightweight levels by applied composite materials.Selective laser melting(SLM)is convenient for integral forming of materials and structures.Hence,in this study,the research about the mechanical response of triply periodic minimal surfaces(TPMS)porous structures with 316 L and composites fabricated by SLM was conducted.The compression test and finite element method(FEM)were used to characterize mechanical properties.The composite structures exhibit enhanced elastic modulus,yield strength,unvaried lightweight level and refined grain microstructure,which are difficult to realize for porous structures made by pure 316 L materials.The elastic modulus,yield strength,plateau stress and energy absorption of composites were 3187.50,67.73,15.24 and 17.09 MJ/m^(3),respectively.