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Handbook Properties and Selection Nonferrous Alloys and Spl Purpose Mtls (1992) WW Part 7

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Tham khảo tài liệu 'handbook properties and selection nonferrous alloys and spl purpose mtls (1992) ww part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | F for 2 h and slowly cooling. However such treatment causes some loss of strength in AZ31B-H24 sheet products. If distortion of part is observed after rough machining the cutting tool should be inspected to ensure that it is sharp and properly ground. If so the size of cut should be decreased. With complex parts or parts machined to extremely close tolerances it may be advisable to stress relieve or if time permits to store parts for 2 or 3 days between rough machining and finishing. Design and Weight Reduction By substituting magnesium alloys for heavier metals such as steel and aluminum alloys many structural parts can be substantially reduced in weight with little or no redesign. This is possible because manufacturing limitations make many parts heavier than necessary. For example for successful filling of the mold a casting may require a minimum wall thickness greater than that dictated by service requirements and the strength of the metal used. Similarly forgings and extrusions sometimes must be made thicker than necessary and the light weight of magnesium can be used to advantage. In many instances a casting forging or extrusion for which magnesium is substituted for a heavier metal can have adequate strength with no increase in wall thickness. In other parts substitution of magnesium may require greater wall thickness and substantial redesign may be necessary in order to realize maximum weight savings. Because strength and stiffness in bending of many structural sections increase approximately as the square and cube of the section depth respectively it is possible to obtain large increases in strength and stiffness with moderate increases in depth and cross-sectional area. When such increases in depth are permissible it usually is economical to redesign the part for magnesium. The greater bulk of the redesigned part reduces local instability and although the saving in weight is less than maximum the reduction in instability allows design simplification and