Surface inclusions and their evolution on strip rolled on CSP line and in following cold rolling process

Abstract

Hot and cold rolled strip samples with surface defects such as black pockmark, sliver and central cracking were collected from a compact strip production line followed by cold rolling. Microstructures and chemical compositions of the strip with defects were studied by scanning electronic microscopy and energy dispersive X-ray spectroscopy. Four typical types of defects on strip including surface spherical mould powder entrapment, centre spherical mould powder entrapment, surface linear mould powder entrapment and centre linear mould powder entrapment were studied by hot and cold rolling experiment in laboratory. It was observed that spherical mould powder entrapment was transformed into the surface black pockmark after the hot rolling and cold rolling process. Centre spherical mould powder entrapment led to central fracture in the hot and cold rolling process. Surface linear mould powder entrapment resulted in sliver and centre linear mould powder entrapment led to severe sliver.     

Structural refinement of cast magnesium alloys

Abstract

The structure of cast magnesium alloys (grain size and precipitate morphology and size) affects the properties of the products and the scope for use of the alloys. The structure can be controlled by minor additions of inoculants, which are largely determined on the basis of the composition of the alloy concerned. The present paper reviews the scientific background of structural refinement by inoculation and its application to Mg–Zn, Mg–Al, and Mg–Al–Si alloys.     

地区电力系统的频率动态过程仿真

针对东北电网辽阳地区系统与主系统的一次解列事故,采用动态潮流法,进行了地区电力系统频率动态过程的仿真研究,对该地区的低频减载方案进行了分析,计算结果说明该方法可以清晰地描述电力系统的频率动态过程,为运行人员进行事故分析提供可靠的依据。     

Effect of treatment variables on size refinement by phosphide inoculants of primary silicon in hypereutectic Al–Si alloys

Abstract

The effects of phosphorus containing inoculant identity/process history, addition level, addition temperature, and contact time on number density N _A of primary silicon particles in small volumes of cast Al–20 wt-%Si are reported. Inoculation replaces the coarse, branched primary silicon otherwise obtained in the upper part of these castings with a uniform distribution of small polyhedral primary silicon particles. The inoculants tested increased in effectiveness in the sequence: die pressed and heat treated Al–Fe–P; die pressed Al–Fe–P; extruded Al–Cu–P; and Al–Fe–P prepared by a proprietary route. This last inoculant gave a maximum N _A at 200 ppm addition level in this volume of melt for a contact time of 10 min at 800°C, and at 10 min contact time for an addition level of 100 ppm at this temperature. An addition temperature of 850°C produced a small reduction in N _A, compared with 750 or 800°C. The significance of these findings is discussed in the context of previously published work and possible mechanisms leading to less effective inoculation at high addition levels and extended contact times.     

Predicting microstructural evolution and yield strength of microalloyed hot rolled steel plate

Abstract

A mathematical model has been developed to optimise process parameters for production of API grade steel plates by thermomechanical controlled processing at a plate mill in Bhilai Steel Plant, India. The model comprises the prediction of the microstructural evolution during hot rolling, the subsequent phase transformation, and, finally, the mechanical properties of microalloyed steels. Effects of chemistry and mill parameters on recrystallisation, grain growth, and precipitation kinetics were taken into consideration to describe the metallurgical processes. . The model has been validated through laboratory experiments as well as full-scale rolling at the plate mill.     

Thixoforming of a novel layered metal matrix composite

Abstract

Thixoforming is a semisolid processing route capable of producing near net shape components with low levels of porosity in a single, rapid operation. It has potential for the processing of aluminium alloy based metal matrix composites (MMCs). In contrast with casting of fully liquid metal, the flow of material into the die in thixoforming is primarily laminar. Thus, a novel layered MMC structure, generated by spray forming, consisting of alternate lamellae of reinforced and unreinforced alloy, might be preserved in thixoforming. The laminated structure is intended to give an increase in toughness, compared to a homogeneously reinforced material. The material was produced by spray forming alternate layers of aluminium matrix alloy 2014 (Al–4Cu–0·8Si–0·8Mn–0·5Mg) and matrix alloy reinforced with ～17 vol.%SiC particles. Following thixoforming, the layered structure was well preserved with good retention of layer integrity and arrangement. Impact measurements for estimating toughness (Charpy and Izod) showed limited improvement with the layered materials, relative to homogeneously reinforced ones. However, in slow crack growth (Tattersall–Tappin tests), toughness was nearly doubled when estimated in terms of an average energy of fracture from the area below the load–crosshead displacement curve. This was attributed to the reduction in the energy of the propagating crack at low strain rates, which led to a greater potential for the structure, and in particular for the unreinforced layer, to stop or slow the crack. Additionally, these layered MMC materials have provided a striking record of the die filling behaviour for metallic materials during thixoforming. The flow pattern is akin to that in conventional hot forging. This may assist in the establishment of design rules for thixoforming dies.     

Effect of heterogeneous deformation on precipitate distribution in Al–3·7Cu and Al–3·8Cu–1·8Mg alloys

Abstract

Cold rolling and hot rolling of solution treated Al–3·7Cu and Al–3·8Cu–1·8Mg alloys were performed to test the effect of inhomogeneous precipitation in shear bands during following aging of the material. The most effective inhomogeneous distribution of particles was observed for samples hot deformed and aged within the temperature range 473–573 K. It was noted that magnesium addition intensifies coarse shear bands development and following coarsening of particles within sheared area.