Evolution of microstructure and texture of AZ80 magnesium alloy under hot torsion with constant decreasing temperature rate

Hot torsion tests for AZ80 magnesium alloy were carried out in the temperature range of 380℃-260℃,with a constant decreasing temperature rate of 10℃/s in order to weaken the basal texture and refine the grains.The results indicated that the average grain sizes were refined forming gradient structure with increasing specimen radial position from center(12.2-5.4μm),and that the initial basal texture intensity of the extruded magnesium alloy was weakened from 46.2 to 8.3.Furthermore,the extension twins(ETs)could be disintegrated from the twins forming separated twins with smaller sizes.Interestingly,ETs with the same twin variant intersecting with each other could be coalesced forming grains with similar orientation,while ETs with different twin variants were separated by twins boundaries contributing to grain refinement.Moreover,in addition to the conventional continuous dynamic recrystallized(CDRX)grains with 30˚orientation rotated around C-axis of the parent grains,CDRXed grains with 30˚rotation around a-axis and random rotation axis were also discerned.Besides,the CDRX evolution induced twins were also elaborated,exhibiting the complex competition between CDRX and twining.Hot torsion deformation with constant decreasing temperatures rate is an effective way of grain refinement and texture modification.

Regional Summer Temperature Decrease against Global Warming in China, Landform Effect?

The data of 16o national meteorological observatory （NMO） stations with long-term monthly temperature data for China were analyzed in this study to show the basin-centered summer temperature decrease against global warming in the past half century. The summer and winter isotherm structures of 1950s and 1990s worked out by interpolation show the isotherm structure variations： the isotherm structure generally moves northward in winter, but in summer it is characterized with separate high-temperature and low-temperature centers and the isotherm structure moves inward the centers with global warming, indicating that the temperature in the highland areas increases but that in the lowland areas decreases in the summer of the duration. The possible mechanism of the basin-centered temperature decrease in summer is discussed in this paper.

Influence of tectonic uplift-erosion on formation pressure

The formation of abnormally low-pressure hydrocarbon reservoirs in petroliferous basins has a close relationship with tectonic uplift and the consequent erosion. In order to understand abnormally low-pressure reservoirs and to provide a scientific basis for exploration and development, we established, through numerical simulation and theoretical analysis, a set of equations for the formation pressure in a closed system influenced by uplift-erosion, discussed the relationship between the genesis of abnormal pressure and uplift-erosion, and put forward the concept of balance pressure （P b ）. The results showed that abnormally high pressure coefficient may form when the current formation pressure was higher than P b , and abnormally low pressure may form when the current formation pressure was lower than P b . In the Santanghu Basin, the current formation pressure of abnormally low pressure reservoirs is lower than P b , so tectonic uplift-erosion leads to the decrease of the pressure coefficient. There is a positive correlation between the pressure drop caused by the decrease of fluid temperature and the rebound of rock porosity and strata erosion. Calculation results indicated that the reservoir pressure of Jurassic strata in the Santanghu Basin was decreased by 11.6-17.1 MPa due to tectonic uplift-erosion during the Late Yanshanian period.

Improved Plasticity and Cold-rolling Workability of Fe–6.5wt%Si Alloy by Warm-rolling with Gradually Decreasing Temperature

The effects of warm-rolling process on the microstructure, ordering, mechanical properties and cold- rolling workability of Fe-6.Swt%Si alloy were investigated, where three processes of warm-rolling with the same total reduction of 93% were used, including （1） 500 ℃/12 passes/total reduction of 93%, （2） 500 ℃13 passes/total reduction of 50% ＋ 400 ℃19 passes/total reduction of 86%, and （3） 500 ℃13 passes/total reduction of 50% ＋ 400 ℃15 passes/total reduction of 60% ＋ 300 ℃14 passes/total reduction of 64%. The results show that compared with process （1） warm-rolling with constant temperature of 500 ℃, process （2） and process （3） warm-rolling with gradually decreasing temperature can significantly improve the room temperature plasticity and cold-rolling workability of the Fe-6.5wt%Si alloy. For example, the three point bending fracture deflections are increased by 54.5% and 81.8% for processes （2） and （3）, respectively, and the maximum reductions of single pass cold-rolling without edge crack are increased from 50% of process （1） to 55% of process （2） and 62% of process （3）, respectively. The plasticity improvement of the Fe- 6.5wt%Si alloy can be attributed to both reductions of surface oxidation degree and order degree of the alloy by warm-rolling with gradually decreasing temperature.