Effect of Two-Stage Aging on Microstructure and Properties of Al-Mg-Si Alloys

The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

A Calculation Model for Cooling Rate of Aluminum Alloy Melts during Continuous Rheo-Extrusion

The melt temperature of aluminum alloys plays a significant role in determining the microstructure characteristic during continuous rheo-extrusion. However, it is difficult to measure the actual melt temperature in the roll-shoe gap. In this work, based on the basic theory of heat transfer, a calculation model for heat transfer coefficient of cooling water/roll interface and melt/roll interface is established. In addition, the relationship between the temperature at the melt/roll interface and the velocity of cooling water is investigated. Combined with the CALPHAD calculation, the melt temperature during solidification in the continuous rheo-extrusion process is calculated. Using this model, the cooling rate of an Al–6Mg (wt.%) alloy melt prepared by continuous rheo-extrusion is estimated to be 10.3 K/s. This model used to determine the melt parameters during solidification provides a reference for optimizing the production process of continuous rheo-extrusion technology.

Study on Acid Fracturing Technology for Carbonate Reservoirs in Ordos Basin

Acid fracturing, a key stimulation technology, has been widely applied in carbonate formations, which have the complex reservoir space and natural fracture. However, the conventional acid fracturing technology has limitations in target reservoir due to serious acid leakage and rapid acid-rock reaction speed. Therefore, a deep-penetration acid fracturing technology was proposed to enhance the stimulation effect. The reservoir basic physical properties, such as permeability and porosity, microstructure characteristic of pore throats, mineral composition, and rock mechanics characteristics, were systemically investigated by a series of laboratory experiments. The acid system was also optimized by evaluating rheological properties and residual acid damage. Furthermore, the most important two parameters of acid fracturing, conductivity and effective acid-etched fracture length, were obtained by numerical simulation with commercial software Fracpro PT. Based on the laboratory studies, the acid fracturing technology was applied in the field, and the production of well increased by 1.7 times after stimulation.