Effect of Ca Addition and Heat Treatment on the A390(S)/AM60(L) Interface Microstructure

Overcasting is a new kind of dissimilar joining technique used to produce the aluminum（solid）/magnesium（liquid） bonding bi-metallic material in this study. For the Al/Mg（A390/AM60） bi-metallic samples, the interface microstructures are the research points, which directly influence the mechanical properties. It is, therefore, of vital importance to find a method to improve the interface microstructures. This research focused on the effect of the calcium（Ca） addition in the liquid Mg alloys and the heat treatment on the A390/AM60 interface microstructures of the bi-metallic samples. The testing results showed that, with Ca addition in AM60, owing to two possible reasons, the interface microstructure and the shear strength of the A390/AM60 bi-metallic samples could be improved. The heat treatment could further improve the interface microstructure and the mechanical properties by dissolving β-Mg_（17）Al_（12） into α-Mg and destroying the Mg_2Si layer structure.

Impacts of heavy metals on 1,2-dichloroethane biodegradation in co-contaminated soil

1,2-Dichloroethane （DCA）, a potential mutagen and carcinogen, is commonly introduced into the environment through its industrial and agricultural use. In this study, the impact of lead and mercury on DCA degradation in soil was investigated, owing to the complex co-contamination problem frequently encountered in most sites. 1,2-Dichloroethane was degraded readily in both contaminated loam and clay soils with the degradation rate constants ranging between 0.370-0.536 week-1 and 0.309-0.417 week-1, respectively. The presence of heavy metals have a negative impact on DCA degradation in both soil types, resulting in up to 24.11% reduction in DCA degradation within one week. Both biostimulation and treatment additives increased DCA degradation, with the best degradation observed upon addition of glucose and a combination of diphosphate salt and sodium chloride, leading to about 17.91% and 43.50% increase in DCA degradation, respectively. The results have promising potential for effective remediation of soils co-contaminated with chlorinated organics and heavy metals. However, the best bioremediation strategy will depend on the soil types, microbial population present in the soil matrices, nutrients availability and metal forms.

Improvement of tensile superelasticity by aging treatment of NiTi shape memory alloys fabricated by electron beam wire-feed additive manufacturing

For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.