The complex processing of carbon fiber requires a high level of expertise, and the BMW Intelligent Lightweight Architecture concept “Carbon core” has been applied for the first time to the new BMW 7 Series, a milestone in automotive engineering that has changed the perception of lightweight technology in this era. It also means better driving comfort and better dynamics.
The use of a high-strength carbon core enables a significant and targeted reduction in body we
ight, while at the same time improving vehicle stability. In terms of torsional stiffness, not only has the body weight been reduced by 130 kg compared to the previous generation, but comfort and safety have also been improved. In addition, the intelligent hybrid structure and weight optimization technology guarantee a consistent weight reduction from the whole to every detail, an almost perfect 50:50 axle load distribution and a further reduction of the center of gravity.
But one of the big challenges that metal materials need to face when connected to carbon fiber composites is electrochemical corrosion.
Electrochemical corrosion occurs when two different metals pass through an electrolyte. Although carbon fiber is not a metal, it is also a good conductor and also has a large potential difference with steel or aluminum alloys. Metal-to-metal corrosion occurs at the metal joints, and although it does not corrode carbon fiber composites, it does erode steel and aluminum alloys. And water is the most common electrolyte.
Therefore, in the new BMW 7 Series, carbon fiber composites are only used in critical structural parts of the car body and in dry areas. In addition, through the structural adhesive, on the one hand to achieve the bonding of different parts, but also to block the path of chemical corrosion of carbon fiber and metal materials, so as to achieve corrosion protection against electrochemical corrosion.
For the joining process of metal and composite materials, in addition to the structural adhesive bonding, it is also necessary to combine it with physical riveting. swimming” concept.
Adhesive riveting process
For the gluing of composite materials and metal parts, because different materials have different coefficients of thermal expansion, the structural adhesive should have good toughness.
In this regard, the swimming process we improve the bonding toughness by increasing the thickness of the structural adhesive.
By increasing the thickness of the structural adhesive, we can achieve better expansion compensation and higher elongation at break, but the bond strength will be reduced and the amount of structural adhesive used will be increased, thus increasing the cost. So it needs to be adjusted according to the actual situation.
