As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In ...As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.展开更多
In the traditional primary school Chinese classroom, there is a serious phenomenon of "indoctrination" teaching, which results in the teaching classroom being stiff and boring. It is not only difficult to st...In the traditional primary school Chinese classroom, there is a serious phenomenon of "indoctrination" teaching, which results in the teaching classroom being stiff and boring. It is not only difficult to stimulate students interest in learning, but also can dampen students enthusiasm for Chinese learning, and even lead to students boredom, which is not conducive to the orderly implementation of reading teaching. At this time, it is necessary for teachers to take the new concept as a guide, actively optimize the means and methods of classroom teaching, and implement teaching in a way that meets the students physical and mental characteristics and actual needs, so that more students can integrate into it independently and obtain all-round development in their own practice. So, in the actual reading teaching of middle and senior grades, what aspects should we start with to achieve the purpose of effective reading teaching? The details are as follows.展开更多
文摘As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.
文摘In the traditional primary school Chinese classroom, there is a serious phenomenon of "indoctrination" teaching, which results in the teaching classroom being stiff and boring. It is not only difficult to stimulate students interest in learning, but also can dampen students enthusiasm for Chinese learning, and even lead to students boredom, which is not conducive to the orderly implementation of reading teaching. At this time, it is necessary for teachers to take the new concept as a guide, actively optimize the means and methods of classroom teaching, and implement teaching in a way that meets the students physical and mental characteristics and actual needs, so that more students can integrate into it independently and obtain all-round development in their own practice. So, in the actual reading teaching of middle and senior grades, what aspects should we start with to achieve the purpose of effective reading teaching? The details are as follows.
