| Magnesium alloys have series of characteristics, such as low density, high specific strength and specific rigidity, good damping performance and electromagnetic shielding characteristics etc. Magnesium alloy die castings have many advantages such as good dimensional stability, high production efficiency, easy processing, and can prolong the service life of the mould because of low adhesion force with mould etc. With the improving of the die casting technology, continuous improvement of die casting equipment and process, many power tool manufacturers want to apply magnesium alloy on the some parts of electric hammer. Not only reducing the weight of the hammers but also damping and reducing consumption, So its electric hammer products will be more competitive in the power tools industry.AZ91D and AM60B magnesium alloys are widely used in the die-casting industry. AZ91D alloy has higher strength but lower toughness; AM60B alloy has better toughness but the strength should be improved. Be the die-casting parts such as crankcase for the using of electric hammer of AZ91D and AM60B alloy, when using the process of electric hammer we found that the crankcase of magnesium alloy was earlier broken than aluminum alloy, leads to electric hammer function loss. So in this paper, Ce-rich mixed rare-earth are added into the AZ91D and AM60B alloys to increase its combination properties, and finally prolong the service life time of electric hammer.In this paper, to get the optimum ratio in the laboratory condition of gravity casting at first by using modern analysis and test facilities such as Optical Microscopy(OM), X-Ray Diffraction(XRD), Scanning Electron Microscopy(SEM) and the test analysis of tensile properties, brinell hardness of alloy. Then study on the influences of RE on the service life of magnesium alloy die casting crankcase which used in the electric hammer by the bench test in the factory die-casting stage, and finally increase combination properties of alloy, prolong the service life time of magnesium alloy die casting.The results shows that in the laboratory condition of gravity casting, adding an appropriate of RE to AZ91D alloy, the α-Mg are finer, the shape of β-Mg17Al12phase changed from a continuous network into fine and dispersive graininess or skeletal shape, at the same time formed a new A14RE phases like acicular shape. When the addition of RE was1.0wt%, the refine and modify effect of AM60B alloy were the best. At the same time, the addition of RE improved the gravity casting mechanical properties of the alloy, when the addition of RE was1.0wt%, the brinell hardness and tensile strength raised to64.6HB and175MPa, improved than originally alloy12.3%and15.9%. In the factory die-casting stage, when the addition of RE is1.0wt%in the AZ91D alloy, the microstructures of magnesium alloy die-castings were refined, the β phase was modified better, the alloy average grain size decreased from35μm to20μm. The brinell hardness and impact toughness of AM60B die-castings raised to70.8HB and11.8J·cm-2, improved than originally die-castings10.5%and34.1%. Finally, the bench endurance time of magnesium alloy die casting crankcase which used in the electric hammer raised to210hours from180hours original.In the laboratory condition of gravity casting, adding an appropriate of RE to AM60B alloy, adding an appropriate of RE to AM60B alloy, the a-Mg are finer, the shape of β-Mg17Al12phase changed from a semi-continuous network into fine and dispersive graininess or skeletal shape. When the addition of RE was1.0wt%, the refine and modify effect of AM60B alloy were the best. The addition of RE improved the gravity casting mechanical properties of the alloy all the same, when the addition of RE was1.0wt%, the brinell hardness and tensile strength raised to55.3HB and152MPa, improved than originally alloy12.2%and18.8%. In the factory die-casting stage, when the addition of RE was1.0wt%and Mg-30RE master alloy was3.3wt%in the AM60B alloy, the microstructures of magnesium alloy die-castings were refined, the β phase were modified better, the β phase of adding Mg-30RE master alloy was finer and distributed more dispersive than the magnesium alloy die-casting of adding RE. The alloy average grain size decreased from35μm to about20pμm. When the addition of Mg-30RE master alloy was3.3wt%, the brinell hardness and impact toughness of AM60B alloy die-castings raised to63.4HB and18.8J·cm-2, improved than originally alloy die-castings14.0%and37.2%, both better than the AM60B alloy die-castings adding1.0wt%RE simply. Failure of die-casting AM60B alloy was brittle fracture. The fracture of AM60B with RE or Mg-30RE master alloy additions obvious features the combination of quasi-cleavage and local gliding fracture. The toughness was improved. Finally, the bench endurance time of adding Mg-30RE master alloy AM60B die casting crankcases which used in the electric hammer raised to390hours from200hours original, and achieved average300hours requirement. |
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