a) (6 marks) Indicate with clearly-stated reasons which aluminum alloy(s) and te
ID: 2087457 • Letter: A
Question
a) (6 marks) Indicate with clearly-stated reasons which aluminum alloy(s) and temper(s) you would choose for i) a welded energy-absorbing bumper system for a lightweight recreational vehicle, i) an automotive wheel which requires significant machining, iii) a pressurized liquid-carrying trailer in the shape of a cylindrical vessel, iv) the outer shell or "skin" of an unpainted house trailer b) (8 marks) Indicate with clear reasons, which steel or other metallic material (completely identified) you would specify for: i) a casting which requires considerable machining, moderate strength and cost, ii) a lightweight casting to which 3 studs of similar material must be welded; some machining required, iii) a casting subject to large impact loads, with some machining required, iv) a casting requiring high compressive strength, low cost and some machining c) (6 marks) Automotive crankshafts can be cast or forged. What physical properties would a design engineer consider in choosing each one? (Production considerations are not to be listed)Explanation / Answer
(a) (i) Wrought Aluminium Alloy 7050 can be used for bumper system of light weight recreational vehicle. It contains huge portion of zinc along with magnesium or magnesium with copper in mixture that enhance different degree of toughness. Those comprising of copper have the highest amount of hardness and have been utilised as construction materials, basically in bumper systems. The copper-void mixtures of the sequence have numerous appealing feature such as superb toughness and superior workability, formability, and weldability
(ii) AlSi7Mg0.3 alloy is the best alloy for automotive wheels where a huge amount of machining is needed. The following properties of Aluminium alloy are considered: Superior metal casting properties, Capability to resist substantial impact, Corrosion resilience, Fatigue resistance. AlSi7Mg0.3 alloy provides the optimum settlement between fatigue stability and elongation. Aluminum has optimistic future in automobile fiels due to huge strength per unit weight ratio.
(iii) Aluminum alloys 5454 are used in pressure vessels. Nickel is added to aluminum-copper to upgrade hardness and toughness at hogher temperatures and to decrease the coefficient of expansion.It is a desirable addition along with iron to improve corrosion resistance to high-pressure cylindircal vessels.
(iv) Wrought Aluminium Alloy 3034 is used when it comes to the application of trailers. Here Manganese is the significant alloying element. As only a restricted amount of manganese can be adequately added to aluminum, manganese is used as a major element in only a less number of alloys. The popular 3003 alloy, is broadly used as a general alloy for medium-toughness applications which need a good formability in outer shell of trailers.
(b) (i) Magnesium die casting alloys have closely arranged hexagonal structure which makes them perfect for the machining process. Significant results are secured when magnesium alloys are machined with tools drafted for machining aluminum. Because of the less resistance to cutting and low heat capacity of magnesium, we use tools with level faces, sharp cutting corners, high relief angles, small rake angles and a geometry that ensures high and smooth chip flow during machining.
(ii) The most widely used light weight casting alloy is Aluminum Alloy 380. It is superior for machining requirements. High-speed steel tools are basically used for machining aluminum. By utilising medium clamping forces we evade the dimensional discrepancy that happen as a result of deformation.
(iii) The material which is subject to large impact loads is an amorphous steel alloy, a hopeful steel alloys constructed from disposition of atoms that diverge from steel's classical crystal-like form, in which iron atoms fill certain locations. SAM2X5-630 possesses the largest elastic point for any steel alloy.
(iv) Inconel is a category of nickel-chromium superalloy. It is differentiated by its huge toughness and very hiogh compressive strength which is not reduced even at high temperatures.
(c) Cast crankshaft is one-time shaping operation,but forged crankshaft should be forged many times. Moreover heat treatment procedure are also not the same. From the view of internal structure, the operation of forged crankshaft is more secure than that of cast crankshaft. Cast crankshafts have a numerous defects such as sand holes and segregation. The internal structure of forged crankshaft is steady and constant. It eliminates raw material defect. So the difference between cast and forged crankshaft is that we can get better internal grain structure and decrease crankshaft failure from forged crankshaft.
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