钣金外壳和铝合金外壳都具有良好的物理性能和化学性能，但它们在一些性能方面存在明显差异。

　　钣金外壳具有很高的强度和刚性，而铝合金外壳相对较软，因此在受到冲击的情况下钣金外壳更能承受压力。此外，钣金外壳的耐腐蚀性也比铝合金外壳要强。

　　铝合金外壳虽然较软，但其强度也很高，并且具有较强的耐磨性。此外，铝合金外壳还具有良好的抗疲劳性能。

　　钣金外壳和铝合金外壳都具有良好的耐久性，但钣金外壳更耐磨，更耐冲击。

　　从上述分析可以看出，钣金外壳具有更好的物理性能和化学性能，而铝合金外壳虽然软，但也具有良好的强度和耐磨性。所以，两种外壳都具有一定的优点，应根据具体情况选择。

　　Both sheet metal casing and aluminum alloy casing have good physical and chemical properties, but there are obvious differences in some properties.

　　The sheet metal casing has high strength and stiffness, while the aluminum alloy casing is relatively soft, so the sheet metal casing can better withstand pressure under impact. In addition, the corrosion resistance of the sheet metal casing is also better than that of the aluminum alloy casing.

　　The aluminum alloy casing is soft, but its strength is also high, and it has strong wear resistance. In addition, the aluminum alloy casing also has good fatigue resistance.

　　Both sheet metal casing and aluminum alloy casing have good durability, but sheet metal casing is more wear-resistant and impact-resistant.

　　From the above analysis, it can be seen that the sheet metal casing has better physical and chemical properties, while the aluminum alloy casing is soft, but also has good strength and wear resistance. Therefore, both casings have certain advantages, and should be selected according to specific circumstances.