EFFECT OF MAGNESIUM ENHANCEMENT ON MECHANICAL PROPERTY AND WEAR BEHAVIOUR OF LM6 ALUMINUM ALLOY
For last several decades aluminium and aluminium alloys are widely used in automotive industries because for their favourable properties like low density (about 2700 Kg/m 3 ), good malleability, high formability, high corrosion resistance and high electrical and thermal conductivity. High machinability and workability of aluminium alloys are prone to porosity due to gases dissolved during melting processes. However, in the engineering application pure aluminium and its alloys still have some problems such as relatively low strength, unstable mechanical properties and low wear resistance. The microstructure can be modified and mechanical properties, wear resistance can be improved by alloying, cold working and heat treatment. In this regards, the present paper reports the influences of enhancement of magnesium contents on the mechanical properties and wear behavior of LM 6 aluminum alloy. Index Terms: LM 6 Aluminum alloy, wear rate 1. Introduction: Aluminium and aluminium alloy are gaining huge industrial significance because of their outstanding combination of mechanical, physical and tribological properties over the base alloys. These properties include high specific strength, high wear and seizure resistance, high stiffness, better elevated temperature strength, controlled thermal expansion coefficient and improved damping capacity (1). These properties obtained through addition of alloying elements, cold working and heat treatment. Alloying elements are selected based on their effects and suitability. For the purpose of understanding their effects and importance, alloying elements for majority of alloys are best classified as major and minor elements, microstructure modifiers or impurities, however the impurity elements in some alloys might be major elements in others (2). LM6 is one of the most important Aluminium alloy falls under Aluminium - Silicon alloying system in which aluminium is the predominant metal and high levels of silicon (4% to 13%) are added that contributes to give good casting characteristics and increases fluidity, by which we can produce castings of thick as well as thin sections according to the required design. Other typical alloying elements are Copper, Magnesium, Manganese, Silicon, Zinc, Iron, Nickel, Lead and Tin.
Synergic effect of reinforcement and heat treatment on the two body abrasive wear of an Al–Si alloy under varying loads and abrasive sizes
In the present study, an attempt was made to examine the synergic effect of SiC particle reinforcement and heat treatment on the two body abrasive wear behavior of an Al–Si alloy (BS: LM13) under varying loads and abrasive sizes. Silicon carbide particles with size 50–80 μm were reinforced in Al–Si alloy, in varying concentration (10 wt% and 15 wt%), by solidification process (vortex technique) and the composite melt was solidified by gravity casting in a cast iron die. The alloy and composites were solution treated at 495 °C for 8 h, quenched in water and aged at 175 °C for 6 h and cooled in air. Two body abrasive wear behaviour of cast and heat-treated alloy and composite, was examined against abrasives of different sizes (40 μm, 60 μm and 80 μm), at varying applied loads (1 N, 3 N, 5 N and 7 N), up to a sliding distance of 108 m. It has been noted that the alloy suffers from higher wear rate than that of composites either in cast or heat-treated conditions, irrespective of applied load and abrasive size. Further, in most of the cases, the wear rate of composite decreases with increase in SiC particle content. Efforts were made to correlate wear behavior of Al alloy and composites in terms of mechanical properties, microstructural characteristics, applied load and abrasive size through an empirical equation.
THE ATLANTIC SLAVE TRADE AND COLONIALISM: REASONS FOR AFRICA’S UNDERDEVELOPMENT?
It is probably an understatement to assert that Africa, the world’s second largest continent, is underdeveloped compared with other continents. Two major exogenous factors often cited for Africa’s development crisis are the so called ‘dual historical injustices’ – the Atlantic slave trade and colonialism. It is often pointed out that while the former almost completely arrested and retarded Africa’s demographical growth for more than three centuries, evoked a perennial state of acrimony and warfare and created a tense and unprecedented atmosphere of insecurity which hindered economic activities and stifled local entrepreneurship and technological drive and dislocated Africa’s socio-economic and political structures and institutions; the latter tied African countries to the apron strings of western imperial powers thereby rendering the pre-conditions necessary for socio-economic and political transformation unachievable. This paper contends that while the history of Africa’s underdevelopment may be traceable to the Atlantic slave trade and colonialism, African leaders had made enormous contributions to the continent’s underdevelopment and backwardness. The paper concludes that irresponsible and irresponsive leadership, vampirism and prodigality, corruption, lack of respect for democratic ideals, insecurity, endemic civil wars, nepotism, etc are the fundamental causes of Africa’s underdevelopment.