汽车材料比例 Polymer/Composite 5% 1977 Polymer/Composite Today 8% Other Aluminum 18% 3% Low-Carbon Hi/Med- Ferrous Other Strength 71% 20% Low-Carbon Steel Magnesium 3% 1% Ferrous 52% Aluminum 8% Lightweight materials can Hi/Med- provide 35-60%weight Strength Steel reduction compared to steel 11% GM汽车材料比例