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304 stainless steel (304SS) and polyethylene terephthalate (PET) were lapped joined by laser conduction welding using a semiconductor laser with a flat-top thermal distribution. Experimental investigation and numerical simulation were conducted to analyze the weld morphology, pores distribution, interfacial microstructure, temperature field, joint strength and fracture behavior of the laser dissimilar joints. Because of the uniform thermal distribution of the laser, the decomposition of the PET base material was well controlled with pore-free joints obtaining at the welding speed over 25 mm/s. Besides, a compound layer was generated at the interface between 304SS and PET with its thickness decreased when the welding speed increased. Chemical reactions and mechanical anchoring were both observed at the interface suggesting a dual joining mechanism. The joint fracture load first increased then decreased with the increased welding speed. Besides, a ductile to brittle failure transition was clearly seen. The underlying mechanism was also discussed.

Ti–6Al–4V alloys have been widely adopted because of their good mechanical properties. TIG welding is a common method for Ti–6Al–4V alloys. However, the high heat input of conventional TIG can lead to a coarsening of grains within Ti–6Al–4V and thus a weaker Ti–6Al–4V weld. This study presents a novel fast-frequency pulsed tungsten inert gas (FFP-TIG) welding technology to fabricate a high-reliability Ti–6Al–4V weld. The effects of fast-frequency pulsed waveforms on microstructures and mechanical properties of Ti–6Al–4V weld samples were uncovered. The arc core diameter of FFP-TIG technology was reduced by 32%–36% compared with that of conventional TIG. The adoption of FFP-TIG decreased the average grain sizes and acicular martensite α′ within the Ti–6Al–4V weld by 47.7% and 40.5%, respectively, which further enhanced the mechanical properties of the corresponding weldments. The hardness, tensile strength, and elongation of Ti–6Al–4V weldments obtained by FFP-TIG were improved by 10.35%, 13.84%, and 304.61% compared with those obtained by conventional TIG, achieving the highest value of 373 HV, 1018.97 MPa, and 4.301%, respectively. This study provides fresh insight into the development and application of high-reliability titanium alloy weldments commonly used in the aviation industry.

Exploring the impacts of human disturbance on ecosystem services (ESs) in karst areas is crucial for regional sustainable management, and China’s ecological conservation red lines (ECRLs) could provide innovative solutions for global biodiversity conservation. However, it remains unclear how the implementation of ECRLs policies will change the mechanism of human disturbance on ESs. Based on the Conversion of Land Use and its Effects at Small Region Extent (CLUE-S) model, we projected land use changes in 2035 under a Business as Usual (BAU) scenario, Ecological Protection (ELP) scenario, and Future City Plan (FCP) scenario in Weining County, China. The Integrated Valuation of Ecosystem Services and Trade-off (InVEST) model was used to quantify six ESs—crop production, water yield, soil conservation, carbon storage, nitrogen export, habitat quality—and total ecosystem services (TES). Then, we analyzed the impacts of human disturbance changes on ESs. Our research showed that under the ELP scenario, the human disturbance index would decrease by 6.18% and increase in soil conservation (0.34%), carbon storage (21.27%), and habitat quality (9.14%) compared with 2015. A greater area of forest and grassland would lead to a reduction in cropland area, which would lower crop production by 20.76%, with water yield and nitrogen export decreasing by 6.63% and 19.91%, respectively, from 2015 to 2035. The ELP scenario would lessen trade-offs between water yield and carbon storage and habitat quality, such that water yield and nitrogen export would be similar. Meanwhile, to ensure future crop production, more attention should be given to the increase in water yield and nitrogen export caused by cropland expansion, especially in its non-karst areas. TES would increase by 9.27%, which is higher than that obtained under either the BAU or FCP scenario. Eco-environmental conservation and restoration policies were proposed to help its regional high-quality development. Our research provides a decision-making basis to evaluate the implementation effects of ECRLs policies in karst areas and inform the directed management of ecosystems by the government.