The effects of rare Earth addition and hot extrusion process on the grain refinement of magnesium alloy were studied. The as-cast Mg-6Al-1Zn (AZ61) alloy had the average grain size of ~ 64 μ m and its microstructure consisted of α-Mg and Mg17Al12 phase. By partial substitution of Al with Gd to reach Mg-4. 8Gd-1. 2Al-1Zn alloy, it was observed that the Mg17Al12 phase disappeared and two new intermetallic phases, i. e. (Mg, Al)3Gd and Al2Gd, were identified. The extrusion process showed significant effects on the shape and size of intermetallics and grain size of the matrix. The grain size of the extruded Mg-6Al-1Zn alloy was refined from 64 μ m to 13. 4 μ m as a result of recrystallization. Regarding the Mg-4. 8Gd-1. 2Al-1Zn alloy, the grain refinement was much more pronounced, where the extruded grain size has been refined from 698 μ m to 2. 4 μ m (extruded at 385 ° C) and 1. 3 μ m (extruded at 320 ° C). This was related to the presence of fine and widely dispersed intermetallic phases. Tensile strength and total elongation of extruded alloys were much higher than their as-cast counterparts and the extruded Mg-6Zn-1Al alloy showed magnificent Mechanical properties. The latter was related to the absence of intermetallic particles, which act as stress risers.

The effects of rare Earth element, erbium (Er) additions on the microstructure and Mechanical properties of Al-15Zn-2. 5Mg-2. 5Cu alloy have been investigated. This new high strength alloy with erbium additions (0. 5, 1. 0, 1. 5 and 2. 0 wt%) was synthesized by liquid metallurgy route followed by hot extrusion. Microstructural characterization was performed using scanning electron microscope and electron probe microanalysis. Significant amount of grain refinement was observed with erbium addition in the hot extruded and heat treated alloy. Tensile test was performed to investigate the effect rare Earth on Mechanical behavior of alloy in as cast and hot extruded condition before and after T6 heat treatment. The combined effect of erbium addition, hot extrusion and heat treatment significantly enhanced the tensile strength of alloy (602 MPa) when compared to the as cast alloy without erbium addition (225 MPa). The strengthening of the alloy was attributed to grain refinement caused by erbium along with hot extrusion and formation of precipitates after T6 heat treatment. Fractograhic investigations revealed that the hot extruded alloy with erbium addition after heat treatment showed uniformly distributed deep dimples exhibiting ductile behavior.

Entropy generation can be caused by the energy transfer from a high-temperature recourse to a low-temperature resource; this is defined by the second law of thermodynamics. This phenomenon can occur for the Earth by transferring the solar energy from the sun to the Earth. The process of entropy generation of the Earth is an important concept for the life of the Earth. This process also has significant effects on the global hydrological cycle, carbon cycle of the Earth’ s atmosphere, and global warming. This paper presents an approximate method to estimate the entropy generation of the Earth caused by the sun. Application of the heat engine to calculate the entropy generation of the planets has been carried out so far. In this research work, the concept of heat engine is applied to calculate the entropy generation of the Earth and the atmosphere surrounding it in a relatively simple Model. Based upon this calculation, the rate of entropy generation of the Earth and its surrounding atmosphere is 6. 5149 × 10 14 𝑊 𝐾 ⁄ . Moreover, by considering this imaginative heat engine, the first and second law efficiencies are equal to 0. 11036 % and 0. 11546 %, respectively. The results of this research work have also been justified by similar works on this topic.